Article

DNA Polymerase Activity Associated with RNA Tumor Viruses

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Abstract

C-type RNA viruses, originating in mouse, cat, hamster, and viper, catalyze the synthesis of DNA from its constituent deoxyribonucleoside triphosphates. Both the rate and extent of the reaction were significantly enhanced by brief treatment of the intact virus with ether. A proportion of the newly synthesized DNA was associated with virions when intact virus was used as template; this was not the case with ether-treated virus. In both cases, DNA extracted from the reaction mixture sedimented slowly, at about 2-4 S.

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... Preliminary evidence indicates its presence in PPV virions also (Stone et al., unpublished data). This enzyme has been found in RNAcontaining avian and murine leukemia-sarcoma viruses (2, 15) as well as in C-type RNA viruses of the cat, hamster, and viper (5). Thus, the polymerase appears to be common to all oncogenic RNA viruses, but is not generally associated with nononcogenic RNA viruses. ...
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Progressive pneumonia virus, the causative agent of a slow, pulmonary disease of Montana sheep, was shown to be antigenically related to two other slow viruses of sheep, visna and maedi. Electron microscopic examination of infected cells revealed that the virus matures by a budding process and that the budding particles as well as the mature, extracellular virions bear striking resemblances to the oncogenic ribonucleic acid (RNA) viruses. Recent findings of an RNA-dependent deoxyribonucleic acid polymerase associated with the virions of this group of slow viruses lend further support to the notion that they may tentatively be classified with the oncogenic RNA tumor viruses.
... It was possible to detect very low levels of virus by measuring deoxyribonucleic acid (DNA) polymerase from culture medium of cells shortly after infection with strain MC29 virus, when the noninfected control cultures showed no enzyme activity (11). These studies and earlier work on DNA polymerase activity from other laboratories (2,(4)(5)(6)(7)(8)(9)(10) encouraged us to investigate the possibility that a similar enzyme activity could be detected in the leukemia of man. This is a report on the initial studies of the DNA polymerase activity in plasma from two cases of chronic lymphocytic leukemia (CLL). ...
Chapter
The biological importance of virion polymerases to the infection process of viruses can be gauged from the fact that many groups of viruses possess virion nucleic acid polymerases of one form or another. A list of those animal RNA virus groups (and their members) shown to possess RNA-directed RNA polymerases (RNA transcriptases) is given in Table 1. Included are representatives of the arena-viruses, bunyaviruses (and bunyaviruslike viruses), orthomyxoviruses, paramyxoviruses, reoviruses (diplornaviruses), and rhabdoviruses. Oncornaviruses and similar virus types (e.g., visna) possess an RNA-and DNA-directed DNA polymerase, otherwise known as a reverse transcriptase (Table 2). Of the various DNA virus groups, the poxviruses and possibly the icosahedral cytoplasmic deoxyriboviruses possess a virion DNA-instructed RNA polymerase (Table 3). Virus isolated from patients with serum hepatitis appears to possess a DNA-directed DNA polymerase.
Article
One or more sulfhydryl (SH) inhibitors usually show greater activity against human and animal solid tumors than against normal tissues in vivo or in radioactive tracer studies in vitro. Selected SH inhibitors inhibit incorporation of thymidine-2-14C into DNA and produce an accumulation of label in thymidine triphosphate in animal and human ascites cancer cells in vitro. The clinically-promising SH inhibitors depress RNA dependent DNA polymerase (‘reverse transcriptase’) activity from Rauscher murine leukemia virus and from lymphoblasts of leukemic patients more than DNA dependent DNA polymerase activity.Copyright © 1972 S. Karger AG, Basel
Article
Tumor growth in NMRI mice infected neonatally with the Moloney murine sarcoma virus was effectively inhibited by an aqueous eluate from the silica gel 'Kieselgel PF 254'. This inhibitory effect was observed whether the silica gel eluate was injected 12 hr before virus inoculation or mixed directly with the virus inoculum. Upon mixing with the Moloney murine sarcoma virus, the silica gel eluate was barely effective if the virus eluate mixture was incubated for only 1 min (at 250) but significantly more effective if the mixture was incubated for 5 min (or more)(at 250), suggesting that the antitumor activity of the eluate was due to a direct inactivating effect on the virus. This virus inactivating effect was equally well expressed in immunocompetent (NMRI) as in immunoincompetent (genetically thymusless nude) mice. The postulated virucidal effect of silica gel eluate appeared to be limited to oncogenic RNA viruses; the eluate did not alter the infectivity of other viruses such as vaccinia, herpes simplex, Newcastle disease, vesicular stomatitis, and polio. The Moloney murine sarcoma virus inhibiting effect of the silica gel eluate might have been related to a stimulatory effect on the RNA dependent DNA polymerase activity of oncogenic RNA viruses, as a markedly increased DNA synthesis was noted in an in vitro DNA polymerase assay with the Moloney murine leukemia virus. However, the silica gel eluate did not affect the integrity of the Moloney murine leukemia virus, as assayed by isopycnic centrifugation of treated and untreated virus particles in a sucrose density gradient.
Article
Mouse mammary tumour virus contains an RNA dependent DNA polymerase. The enzyme requirements and physical properties of the reaction products are similar to those of other RNA tumor viruses, despite the unique characteristics of the virus in other properties.
Article
A study was made of the DNA polymerase of reptilian type C virus isolated from Russell's viper spleen cells. Simultaneous detection experiments demonstrated the presence of 70S RNA and RNA-dependent DNA polymerase activity in reptilian type C virions. The endogenous activity was dependent on the addition of all four deoxynucleotide triphosphates and demonstrated an absolute requirement for a divalent cation. The reptilian viral DNA polymerase elutes from phosphocellulose at 0.22 M salt. In this respect, it is similar to the avian (avian myeloblastosis virus; AMV) viral enzyme but is different from the mammalian (Rauscher leukemia virus; RLV) viral enzyme which elutes at 0.4 M salt. The molecular weight of the viper DNA polymerase as estimated from glycerol gradient centrifugation is 109,000. It is a smaller enzyme than the AMV DNA polymerase (180,000 daltons) and somewhat larger than the RLV enzyme (70,000 daltons). A comparison of other properties of the type C reptilian DNA polymerase with the enzyme found in other type C oncogenic viruses is made.
Article
Infectious hamster leukemia virus (HaLV) contains a DNA polymerase different from those of murine and avian viruses. No endogenous reaction directed by the 60 to 70S RNA of HaLV could be demonstrated in detergenttreated HaLV virions, nor could the purified DNA polymerase copy added viral RNA. The virion RNA could, however, act as template for added avian myeloblastosis virus DNA polymerase and the HaLV DNA polymerase could efficiently utilize homopolymers as templates. The HaLV enzyme was like other reverse transcriptases in that certain ribohomopolymers were much better templates than the homologous deoxyribohomopolymers. No ribonuclease H activity could be shown in the HaLV enzyme, but neither could activity be found in the murine leukemia virus DNA polymerase. The hamster enzyme was unique in that poly(A) .oligo(dT) was a poor template, and globin mRNA primed with oligo(dT) was totally inactive as a template. Its uniqueness was also indicated by its subunit composition; electrophoresis of the HaLV DNA polymerase in sodium dodecyl sulfate-containing polyacrylamide gels revealed equimolar amounts of two polypeptides of molecular weight 68,000 and 53,000. The sedimentation rate of the enzyme in glycerol gradients was consistent with a structure containing one each of the two polypeptides. The enzyme thus appears to be structurally distinct from other known virion DNA polymerases. Its inability to carry out an endogenous reaction in vitro might result from an inability to utilize certain primers.
Article
Successful transmission of murine leukemia by the passage of cell-free filtrates from leukemic tissue was first described in 1951. Viruses have subsequently been shown to be causally related to a wide variety of leukemias and lymphomas in many different mammalian species. Many of these viral agents were initially derived from tumors other than leukemias and some of them induce neoplasias uncharacteristic of those generally seen in nature. Others, however, were recovered initially from spontaneous or induced leukemias and induce similar tumors in the recipients. Still a third group of viruses were derived from apparently the normal tissues and were found to be capable of inducing leukemias or lymphomas either in the same or in a different genus or species of mammal. In these instances, the viral genetic information may vary from being unexpressed, partially or fully expressed. When viral information initially present in covert form becomes expressed in overt form, the process can be described as virus activation or induction. Many events, both physiological and pharmacological, are associated with the activation of leukemia viruses in vivo and in vitro. Among these events are radiation, treatment with hormones or chemicals, certain specific immunological reactions, and sometimes even aging itself. This chapter covers in vivo and in vitro activation of endogcnous mammalian leukemia viruses, both descriptively and analytically. It attempts to relate the phenomena described both to the current theories of viral oncogenesis and to the pathogenesis of mammalian cancer.
Article
DNA polymerase activity has been separated from intact virions and is found associated with the nucleoid. Antiserum to the viral proteins inhibits this activity.
Article
The specificity of the DNA product of the RNA-dependent DNA polymerase found in C-type virions was analyzed by reciprocal hybridization with RNA from viruses of mouse, hamster, cat, and viper. These tests revealed a clear species specificity for the DNA product with no detectable interspecies hybridization.
Article
DNA polymerase activity was found in chick embryo cells (CEC) that were infected with a tumor virus, strain MC29 (myelocytomatosis) virus. The enzyme activity in homogenates of virus infected cells was greater than in homogenates from noninfected control cells.DNA polymerase activity from noninfected CEC was not able to use the homopolymer duplex, poly dC:poly rG as a template. However, polymerase in cells infected with tumor virus was able to utilize this homopolymer duplex as template, as was the DNA polymerase associated with MC29 virus.The results demonstrated that DNA polymerase activity found in MC29 virus was detectable in the infected-cell homogenate and was distinguished from the cell DNA polymerase by its ability to utilize dC:rG as template.
Article
In vitro RNA synthesis is catalyzed by an enzyme found in purified virions of each of nine influenza strains tested. The extent of [(3)H]UTP incorporation observed is strain dependent, with an obligate requirement for Mn(2+) ions and RNA template. At least 30% of purified product RNA shows resistance to degradation by ribonuclease A and T1 before and after annealing with exogenous RNA from influenza virions.
Article
Sera from rats bearing transplantable tumors induced by murine C-type tumor viruses contain an inhibitor of the activity of the viral RNA-dependent DNA polymerase. The inhibitor is shown to be an immunoglobulin (IgG) directed against the enzyme. Antiserum made in rabbits against partially purified murine leukemia virus polymerase also inhibits the polymerases of other mammalian C-type RNA-containing tumor viruses. Thus, the polymerases from different mammalian tumor viruses are antigenically related.
Article
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Article
Ethidium bromide, compared on a molar basis, was a more effective inhibitor of the DNA polymerases of the Rauscher and Moloney murine leukemia viruses than either 4-N-demethylrifampicin or 4-N-benzyldemethylrifampicin. Daunomycin inhibited the polymerases weakly, and chromomycin A(3) inhibited almost not at all. 4-N-Benzyldemethylrifampicin was a more active inhibitor than the 4-N-demethyl congener.
Article
Extraction of avian myeloblastosis virus with phenol and SDS and electrophoresis of the proteins on polyacrylamide gels resulted in a variety of components. Four major bands were detected by protein specific staining and their molecular weights were estimated to be 13,000, 15,000, 23,000, and 28,000. These components were shown to be present in virus from both subgroup A and B. One of these (15,000 mol. wt.) demonstrated exceptional staining properties with amido black but incorporated radioactive amino acids poorly. Another component (23,000 mol. wt.) showed a tendency to aggregate which could be eliminated by use of dithiothreitol. In addition to these major components a series of smaller bands of higher molecular weight were detected. The most distinct of these (115,000 mol. wt.) seemed to be associated with material which could be stained for polysaccharide and was strongly labeled with glucosamine-14C. A similar component was also found in preparations known to contain the type-specific antigen of the virus. The various components could be recovered following preparative electrophoresis enabling immunological analysis to be performed (Bauer and Bolognesi, this series, Part II, see following article).
Article
The availability of a purified RNA-instructed DNA polymerase (reverse transcriptase) from avain myeloblastosis virus provided the opportunity to explore whether this enzyme could be used as a general tool for synthesizing DNA complements of a wide variety of natural RNAs. The results described show that this potentially useful situation is in fact realized. The avian viral transcriptase can mediate the synthesis of DNA complementary to RNAs of such widely divergent origins as Qβ bacteriophage and Moloney sarcoma virus. These findings open up novel pathways for the experimental resolution of several interesting problems. Thus, given a purified RNA message, one should be able to synthesize the corresponding DNA genetic material. If suitably labeled, the synthetic DNA has various obvious uses, including its use via molecular hybridization as an analytical probe for the corresponding gene on the chromosomes or for its message in a complex mixture of RNA molecules. Of immediate practical interest is the import of these findings for viral oncology. They imply that for many purposes we will not be compelled to isolate or use the “reverse transcriptase” from each oncogenic virus in order to synthesize its complementary DNA. The ability of one enzyme to accept a variety of oncogenic RNAs will obviate many of the logistical difficulties that arise, particularly in attempts to illuminate the etiology of human cancer.
Article
Tumor virus RNAs from several mammalian and one reptilian species were purified; their 3'-terminal nucleoside was identified by separation of the trialcohols produced by periodate oxidation followed by reduction and tritiation with NaB(3)H(4). Each virus contained uridine as the predominant terminal nucleoside. Molecular weight estimations based on the tritiation reactions were consistent with a structure consisting of four subunits.
Article
Inhibition of the ribonucleic acid (RNA)- and deoxyribonucleic acid (DNA)-dependent DNA polymerase activities of mammalian C-type viruses was obtained with sera from rats bearing murine leukemia virus-induced transplant tumors. Polymerase activities of nonmammalian (viper) C-type virus and murine mammary tumor virus were not inhibited by such sera nor by serum from a rat immunized with the DNA polymerase of feline leukemia virus purified by isoelectric focusing. The latter serum appeared to inhibit preferentially the DNA-dependent DNA polymerase activity of mammalian C-type viruses showing no inhibition of RNA-dependent DNA synthesis.
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Several properties of the viral RNA-dependent DNA polymerases and of rabbit globin mRNA make it possible to consider synthesis of the globin gene in vitro. These enzymes copy an RNA template using a short sequence of complementary nucleotides as a primer. Furthermore, globin mRNA has a 3'-terminal sequence of adenylic acid residues that make it particularly suitable as a template, since oligo(dT) can be annealed to a specific site on the mRNA. This small primer could phase the DNA polymerase, possibly ensuring that replication is initiated from that end of the globin message. We have used this approach and find that purified mRNA is an efficient template for the polymerase enzyme. The reaction requires the RNA template and the four deoxyribonucleoside triphosphates, and it is markedly stimulated by the addition of oligo(dT). Consistent with the expectation that the oligo(dT) uniquely phases the polymerase at an adenine-rich region in the globin message, oligo(dG), oligo(dC), and oligo(dA) fail to serve as primers. The product has a density intermediate between that of DNA and RNA, and shifts to a lighter DNA density after treatment with base. Further, it is specifically complementary to globin mRNA and sediments slightly faster in an alkaline sucrose gradient than a DNA standard that has a molecular weight of 129,000. The data suggest that a major portion of the DNA product is a sequence of at least 500 bases, about 50 more than would be necessary to encode rabbit globin. The potential usefulness of this interesting product is discussed.
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Reticuloendotheliosis virus (REV) was purified from liver and spleen homogenates and chick embryo fibroblast Rollacell cultures by a series of differential, velocity, and sucrose density-gradient centrifugation methods. This enveloped virus was found to have the following properties: 1) a diameter of approx. 100 nm; 2) a buoyant density in sucrose of 1.16-1.18 g/cc; 3) single-stranded RNA at a concentration of approx. 7-8%; and 4) DNA polymerase activity.
Article
Monospecific antiserum was prepared against purified deoxyribonucleic acid (DNA) polymerase from avian myeloblastosis virus (AMV). Immunodiffusion assay with purified DNA polymerase revealed that the anti-DNA polymerase serum formed one precipitation band, whereas no reaction with any of the seven major structural proteins of AMV was observed. The antiserum also demonstrated enzyme-neutralizing antibody activity that was associated with the immunoglobulin G fraction. There was no difference in the neutralization of DNA polymerase activity directed by ribonucleic acid (RNA), DNA, or RNA-DNA hybrid templates.
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Bovine adenovirus type 3 (BAV-3), strain WBR-1, quantitatively transforms hamster embryo carcass cells with a maximum efficiency of 4-7 X 10-4 p.f.u./focus-forming units (f.f.u). This frequency is signigicantly inhibited by the presence of 1-8 mM of Ca++. The transformed cells are highly tumourigenic in hamsters and possess T- and tumour-specific transplantation antigens. BAV-3 is one of the most oncogenic of the adenoviruses and an ideal model virus for the study of transformation.
Chapter
More than four years have passed since University of Wisconsin Virologist HOWARD M. TEMIN disclosed at the 10th International Congress of Cancer that he and his coworkers had found preliminary evidence for an enzyme that permits ribonucleic acid (RNA) to dictate the synthesis of deoxyribonucleic acid (DNA). Independently the same phenomenon was observed by DAVID BALTIMORE (1970b) of the Massachussetts Institute of Technology. Although perhaps not as fundamental a concept as the α-helical structure of DNA, the RNA-dependent DNA polymerase (reverse transcriptase) is a concept that is shedding light on several unexplained biological phenomena and has already inspired biochemists, molecular biologists, virologists and even biophysicists to look into the mystic of this process. Thus, TEMIN’s discovery of “backward” transcription has set off an explosive and still unforseeable burst of activity in numerous laboratories.
Chapter
The Central Dogma of molecular biology which postulates the unidirectional transmission of genetic specifications for protein biosynthesis was enunciated by Crick (1958) who proposed explicitly that “once ‘information’ has passed into protein it cannot get out again. In more detail, the transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein or from protein to nucleic acid is impossible. Information means here the precise determination of sequence either of bases in the nucleic acids or of amino acids in the protein.”
Chapter
Folgende Grunde und Gesichtspunkte rechtfertigen gerade auch im Hinblick auf den eigentlichen Zweck der experimentellen Krebsforschung, namlich der Krebsbekämpfung beim Menschen zu dienen, eine ausfuhrlichere Darlegung der murinen Leukamien und der sie verursachenden (onkogenen) Viren: 1) In den letzten Jahrzehnten — seit der wichtigen Entdeckung des Virus der lymphatischen Leukamie der Maus durch L. GROSS (1951) — wurde eine Vielzahl weiterer Leukämieviren bei der Maus nachgewiesen, die bei dieser Tierart und z.T. auch bei der Ratte hamatologisch sehr differente Leukämietypen (myeloische, retikulare, erythroblastische Leukämien) verursachen.
Chapter
Neoplasia, though still not thoroughly understood, has been of medical importance since the beginning of recorded history and, undoubtedly, before that. Cancer in man presently ranks as the second largest killer, lagging only behind cardiovascular disease. As a consequence of its obvious impact on human life, millions of dollars and countless research hours have been dedicated to determining causes, treatments and preventions for this dread disease. This interest has spilled over into the comparative study of neoplastic disease in the higher vertebrates. Until the last 50 years, however, coldblooded vertebrates were neglected in such investigative studies even though more than a century and a half ago the question of brute creatures being subject to diseases resembling cancer in man was posed (Baillie et al., 1806). The fear and disgust for reptiles was documented with Adam and Eve and has been perpetuated to this day, probably contributing to the paucity of studies in reptilian diseases.
Chapter
Thomas Hodgkin (1832) identified lymphoid neoplasia as a disease entity in man 146 years ago. His description served to focus attention on disorders arising within the lymphoid tissue as distinguished from those beginning elsewhere and only secondarily involving these areas. A very mixed assortment of diseases were first grouped together. Some were true lymphoid malignancies, others were not. In retrospect, at least three of Hodgkin’s original patients had tuberculosis rather than tumors (Fox, 1926). Nonetheless, the process of identifying lymphoid malignancies was begun. The subsequent sorting, describing, and classifying continues today.
Chapter
Viruses have been shown to share unique properties, which may help in finding approaches for elucidation of the patterns of their gene expression and regulation. This chapter discusses these approaches for five groups of large RNA viruses of animals, such as reoviruses, rhabdoviruses, paramyxoviruses, myxoviruses, and oncornaviruses. These groups differ significantly from each other in structure and mechanisms of replication. Reoviruses represent a unique group of viruses with the segmented double-stranded RNA genome. Unlike the other four groups, they have an icosahedral type of subunit arrangement and lack a lipid-containing envelope. The genome of rhabdoviruses and paramyxoviruses is a continuous single-stranded RNA, whereas the genome of myxoviruses and oncornaviruses consists of several separate segments. Oncornaviruses differ from the four other groups by their unique mode of reproduction, involving the synthesis of DNA. The aim of this chapter is to review present knowledge concerning involvement of viral cores and nucleocapsids in transcription in and in vivo and to discuss the possibility that nucleocapsids represent functionally active units in this process. These sections are preceded by a section where structure, composition, and some properties of cores and nucleocapsids are briefly summarized, the data being used for further discussion. Finally, this chapter includes a section concerning some aspects of template-enzyme interactions.
Chapter
This chapter provides description of the properties and classification of the oncornaviruses and related virus particles that possess RNA→DNA polymerase molecules. The chapter describes the properties of the DNA polymerase activities of oncornaviruses and related particles including the endogenous reaction, the reaction products, and the utilization of external templates. The chapter also deals with the studies on the inhibitors of the viral DNA polymerase, their mechanism of action and their effect on cell transformation and tumor induction. The properties of purified RNA→DNA polymerase and the mechanism of DNA synthesis are also explored. The chapter provides evidence for the in vivo function of the viral RNA→DNA polymerase and a concise description of the present understanding of the molecular events of oncornavirus replication and cell transformation. The chapter also discusses the analysis of viral related base sequences in normal and cancer cells by molecular hybridization with the viral DNA product of the RNA→DNA polymerase, and studies on RNA→DNA polymerase in normal and cancer cells.
Article
The potentiality of RNA tumor viruses in human malignancy is discussed to include inhibition of the expression of proviral DNA and formation. Inhibition of oncornaviral DNA polymerase is produced by six mechanisms: enzyme-binding, substarte analogues, template-primer analogues, template binding compounds, divalent cation-binding agents and various miscellaneous sites.
Article
Full-text available
Lymphoreticular proliferative disorders are described in two lizards. The first case, in an East Indian water lizard, Hydrosaurus amboinensis, was classified as a diffuse type of malignant lymphoma of lymphoblastic cell type and is the first known example of a hematopoietic neoplasm in a lizard (class Reptilia; suborder Sauria). The second case, in a Malayan monitor, Varanus salvator, also presented features characteristic of a generalized lymphosarcomatosis, but granulomas associated with a disseminated bacterial infection complicated the picture and precluded an incontestable diagnosis.
Article
A retrovirus previously isolated from a tumored Russell's viper is shown by molecular hybridization to be an endogenous virus of this reptilian species. Radio-immunologic techniques revealed that the viper retrovirus is immunologically and, hence, evolutionarily related to endogenous type D retorviruses of Old World primates. These findings extend the number of vertebrate classes possessing endogenous retroviruses and suggest that type D retroviruses may even be more widely distributed in nature than type C retroviruses.
Article
A soluble DNA polymerase activity is present in plasma of leukemic guinea pigs, and absent in plasma of normal animals. A good correlation exists between the amount of the polymerase activity in plasma and the progression of disease.
Article
1.1. Leukaemic guinea-pig lymphoblasts contain two DNA polymerase activities—one located in cytoplasm and the other associated with nucleus. The nuclear enzyme has been solubilized by sonication. Both DNA polymerases have been partially purified.2.2. There are no qualitative differences between the nuclear and cytoplasmic enzymes.3.3. Both require Mg2+, a sulphydryl compound, and DNA template for optimal activity.4.4. They exhibit maximum activity at pH8.0.5.5. Both enzymes are inhibited by actinomycin-D, mitomycin-C, and high concentrations of NaCl.6.6. Activated DNA acts as the best template for both enzymes.7.7. The products of in vitro reaction of cytoplasmic and nuclear polymerases have been characterized by cesium chloride density gradient and by hydroxylapatite chromatography and have the properties of a partially single- and partially double-stranded DNA. The newly synthesized DNA have sedimentation coefficient of 3–4S in alkaline sucrose gradient.
Article
Abstract Recognition of RNA tumor viruses as causative agents of malignant disease started with the observation (by Ellerman and Bang in 1908) that a filterable agent transmitted avian leukemia1 and the subsequent isolation of chicken sarcoma virus by Rous in 1911.2 These findings were followed by an intense and continuous search for new isolates, the establishment of inbred strains of mice, and the development of tissue culture techniques. In the early 1960s, the significance of RNA tumor viruses was generally accepted, especially in avian and murine systems, but with some skepticism, probably because its role in natural disease was not yet evident. Moreover, the mode of replication of the RNA tumor viruses was still not understood. In recent years, the study of these viruses markedly intensified, principally because of a discovery which filled a major gap in the understanding of their replication. This is the independent discovery of the viral RNA-dependent DNA polymerase (reverse transcriptase) by Temin and Mizutani3 and by Baltimore4 in 1970. This discovery also extended our understanding of the mode of genetic information transfer, and it paved the way for the finding of viral-related components, reverse transcriptase5-11 and type-C viral related nucleic acids in human leukemic cells by Gallo, Spiegelman, and their co-workers (see later section10,12-17).
DNA polymerase from avian myeloblastosis virus has been purified by a combination of column chromatography and gel filtration methods. The isolated enzyme sediments at approximately 6 S and consists of two subunits of molecular weights 110 000 and 69 000. It is free of RNA and DNA endonuclease activity. The enzyme possesses the RNA-, DNA-, and hybrid-directed polymerase activities found in the virion.
Article
9-O-methyloximd erythromycin A and its analogue inhibited reverse transcriptase and blocked focus formation of Rous sarcoma virus. These chemicals inhibited neither DNA-dependent DNA polymerase nor DNA-dependent RNA polymerase from bacterial sources. However, they inhibited reverse transcriptase with an apparently differnt mechanism than that by rifamycin ABDP.
This chapter discusses the immunological and chemotherapeutic prevention and control of oncogenic viruses. The development of in vitro (tissue culture) assay systems has facilitated the rapid testing of drugs and other potentially active antiviral agents. In addition, these assays have been found useful in studies designed to elucidate the mechanism of inhibitory action of antiviral agents. Murine leukemia viruses are assayed by the XC-test, in which a quantitative number of syncytia are formed. Infective titers of murine sarcoma virus can be quantitated by the number of foci formed on mouse embryo fibroblast cultures. These assays have shown to be useful for isolating naturally occurring viruses of the murine leukemic group in tissue culture and for determining the helper role that murine leukemia viruses possess for defective murine sarcoma virus. Several murine leukemia and sarcoma virus-transformed cell lines have been established and have been employed for testing drugs. An alkaloid extract of the Narcissus bulb and rifampycin derivatives have been shown to exert an in vitro inhibitory effect on murine leukemia and sarcoma virus replication.
Article
The considerable efforts in recent years to determine an etiology of human cancer with its importance for early diagnosis, prophylaxis, and therapy have associated, with increasing frequency, RNA tumor viruses with some human malignancies. Early electron microscopic and immunologic studies gained new significance with recent biochemical evidence: the discovery of an RNA-directed DNA synthesizing polymerase in RNA-tumor viruses and the elucidation of RNA tumor viral replication and transformation properties provided new techniques for the discovery of RNA tumor viruses and their association with human neoplasms.
Article
The reptilian DNA-containing viruses include papovaviruses, iridoviruses and herpes viruses. The RNA viruses of reptiles currently include a myxovirus, 4 leukoviruses, numerous togaviruses, 2 rhabdoviruses and a reovirus. Several cell virus systems have been identified in which the phylogenetic distance between the natural virus host and the experimental host cell is uniquely great. These systems may offer rewarding opportunities for the study of the effect of temperature and host cell on virus replication, virus effects on host cells, phenotypic mixing, viral latency and attenuation of viruses.
Article
Antiserum to partially purified reverse transcriptase from the Schmidt-Ruppin strain of Rous sarcoma virus has been prepared and characterized. Antibody to the avian polymerase inhibited the reverse transcriptase activity of avian C-type viruses but had no effect on the polymerase activity from C-type viruses of other classes. The known mammalian C-type viral polymerases were significantly inhibited only by the antiserum to murine C-type viral polymerases; reverse transcriptases from four other mammalian viruses were immunologically distinct from both avian and mammalian C-type viral polymerases. Partially purified murine leukemia viral DNA polymerase activity was comparably reduced by specific antibody regardless of the template used for enzyme detection.
Article
Two independent groups of investigators have found evidence of an enzyme in virions of RNA tumour viruses which synthesizes DNA from an RNA template. This discovery, if upheld, will have important implications not only for carcinogenesis by RNA viruses but also for the general understanding of genetic transcription: apparently the classical process of information transfer from DNA to RNA can be inverted.
Article
In vitro RNA synthesis is catalyzed by an enzyme found in purified virions of each of nine influenza strains tested. The extent of [(3)H]UTP incorporation observed is strain dependent, with an obligate requirement for Mn(2+) ions and RNA template. At least 30% of purified product RNA shows resistance to degradation by ribonuclease A and T1 before and after annealing with exogenous RNA from influenza virions.
Article
Electron microscopic studies on tissues and cell cultures derived from a tumor-bearing Russell's viper revealed a “C”-type, budding virus associated with the spleen cell line in late passage. Virions have not been observed in the primary tissues, the edematous myxofibroma, or other culture lines to date. The virions were approximately 108 mμ, membrane bound, and possessed a dense nucleoid. These observations support the extension of the range of this family of presumably RNA-containing viruses into the cold-blooded vertebrate group.
Article
Hamster sarcomas induced by the Gross pseudotype of Moloney sarcoma virus yielded a virus sarcomagenic for hamsters but not mice. This virus was able to produce foci on hamster embryo cells, but not on mouse embryo cells. A hamster-tropic nonfocus-forming helper virus was also found in the viral stocks. These hamster-tropic viruses are not immunologically related to the murine viruses in the original inoculum but appear to represent indigenous C-type RNA viruses of the hamster.
Article
An infectious C-type feline sarcoma virus (FSV), isolated from a naturally occurring fibrosarcoma of a domestic house cat, produces fibrosarcomas in kittens and puppies and induces cell transformation in feline embryo fibroblasts. Prenatal inoculation of cat and dog foetuses is particularly effective in tumour transmission. Postnatal dogs bearing FSV induced fibrosarcomas provide antisera suitable for detecting the feline C-type RNA tumour virus antigens in the complement fixation test.
Article
The rate of DNA chain growth was measured in Chinese hamster cells in culture by the use of the density label [3H]bromodeoxyuridine and an inhibitor of thymidylate synthesis, fluorodeoxyuridine. After 5 to 15 minutes of growth in which the analog was substituted for thymidine, the DNA was extracted, sheared and banded in a CsCl gradient. On the basis of the ratio of label in fully substituted DNA fragments to that in partially substituted ones produced by breakage across junction points between segments of bromouracil hybrid and unsubstituted DNA, the rates of DNA chain growth were estimated. In cells growing under the best conditions, the chains appear to be growing at the rate of 1 to 2 μ per minute. For periods of growth that allow the substituted segments to become about twice the length of the fragments produced by shear, the bromouracil-substituted segments are broken nearly at random interstitially and across the junction points with unsubstituted DNA. However, after longer intervals, the indications are that breakage across junctions may be non-random in that some junctions are less susceptible to breakage by shear than regions between junctions. The suggestion is made that these may represent junctions between units of replication (replicons). Since larger segments of chromosomes or whole chromosome arms in some cases incorporate [3H]thymidine for only about three hours in a replication cycle, the maximum size of a replicon in such regions would be the amount of DNA which can grow at the measured rate of 1 to 2 μ per minute in that time. However, some of the gradient profiles reveal a high proportion of partially substituted DNA with bromouracil segments only 1 to 2 μ long. Therefore, the large continuous pieces of DNA in chromosomes may be assembled by the end-to-end joining of rather small subunits during replication.
This work was supported by contract NIH 69-97 of the Special Virus Cancer Program of the National Cancer Institute
* This work was supported by contract NIH 69-97 of the Special Virus Cancer Program of the National Cancer Institute, National Institutes of Health, Bethesda, Md. 'Temin, H. M., and S. Mizutani, Nature, 226, 1211 (1970).
  • M B Gardner
  • R W Rongey
  • P Arnstein
  • J D Estes
  • P S Sarma
  • R J Huebner
  • C G Rickard
Gardner, M. B., R. W. Rongey, P. Arnstein, J. D. Estes, P. S. Sarma, R. J. Huebner, and C. G. Rickard, Nature, 226, 807 (1970).
CorrectionFatty Acid Synthetase Activity in Mycobacterium phlei: Regulation by Polysaccharides, the data given in Table 1, columns 4 and 5, should be reversed (see p. 89) The values in these two columns should read: Glucose 6-O-Methylglucose PSI 0
  • M Ilton
  • A W Jevans
  • E D Mccarthy
  • D Vance
  • H B White
  • Konrad Bloch
Correction. In the article "Fatty Acid Synthetase Activity in Mycobacterium phlei: Regulation by Polysaccharides," by M. Ilton, A. W. Jevans, E. D. McCarthy, D. Vance, H. B. White, III, and Konrad Bloch, which appeared in the January 1971 issue of Proc. Nat. Acad. Sci. USA, 68, 87-91, the data given in Table 1, columns 4 and 5, should be reversed (see p. 89). The values in these two columns should read: Glucose 6-O-Methylglucose PSI 0
the following correction should be made
  • R V Huebner
  • Gilden
Huebner, and R. V. Gilden, which appeared in the September 1970 issue of Proc. Nat. Acad. Sci. USA, 67, 143-147, the following correction should be made: page 143, line 4 from bottom, 0.8 mM, not 8 mM. Corrections 1089