Ichizo Kobayashi

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (103)539.48 Total impact

  • Kyungtaek Lim, Ichizo Kobayashi, Kenta Nakai
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    ABSTRACT: Translation initiation depends on the recognition of mRNA by a ribosome. For this to occur, prokaryotes primarily use the Shine-Dalgarno (SD) interaction, where the 3' tail of small subunit rRNA (core motif: 3'CCUCC) forms base pairs with a complementary signal sequence in the 5' untranslated region of mRNA. Here we examined what happened to SD interactions during the evolution of a cyanobacterial endosymbiont into modern plastids (including chloroplasts). Our analysis of available complete plastid genome sequences revealed that the majority of plastids retained SD interactions but with varying levels of usage. Parallel losses of SD interactions took place in plastids of Chlorophyta, Euglenophyta, and Chromerida/Apicomplexa lineages, presumably related to their extensive reductive evolution. Interestingly, we discovered that the classical SD interaction (3'CCUCC/5'GGAGG (rRNA/mRNA)) was replaced by an altered SD interaction (3'CCCU/5'GGGA or 3'CUUCC/5'GAAGG) through coordinated changes in the sequences of the core rRNA motif and its paired mRNA signal. These changes in plastids of Chlorophyta and Euglenophyta proceeded through intermediate stages that allowed both the classical and altered SD interactions. This coevolution between the rRNA motif and the mRNA signal demonstrates unexpected plasticity in the translation initiation machinery.
    Molecular Biology and Evolution 04/2014; · 10.35 Impact Factor
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    ABSTRACT: Epigenetic modifications such as DNA methylation have large effects on gene expression and genome maintenance. Helicobacter pylori, a human gastric pathogen, has a large number of DNA methyltransferase genes, with different strains having unique repertoires. Previous genome comparisons suggested that these methyltransferases often change DNA sequence specificity through domain movement-the movement between and within genes of coding sequences of target recognition domains. Using single-molecule real-time sequencing technology, which detects N6-methyladenines and N4-methylcytosines with single-base resolution, we studied methylated DNA sites throughout the H. pylori genome for several closely related strains. Overall, the methylome was highly variable among closely related strains. Hypermethylated regions were found, for example, in rpoB gene for RNA polymerase. We identified DNA sequence motifs for methylation and then assigned each of them to a specific homology group of the target recognition domains in the specificity-determining genes for Type I and other restriction-modification systems. These results supported proposed mechanisms for sequence-specificity changes in DNA methyltransferases. Knocking out one of the Type I specificity genes led to transcriptome changes, which suggested its role in gene expression. These results are consistent with the concept of evolution driven by DNA methylation, in which changes in the methylome lead to changes in the transcriptome and potentially to changes in phenotype, providing targets for natural or artificial selection.
    PLoS Genetics 04/2014; 10(4):e1004272. · 8.52 Impact Factor
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    ABSTRACT: Restriction-modification systems consist of genes that encode a restriction enzyme and a cognate methyltransferase. Thus far, it was believed that restriction enzymes are sequence-specific endonucleases that introduce double-strand breaks at specific sites by catalysing the cleavages of phosphodiester bonds. Here we report that based on the crystal structure and enzymatic activity, one of the restriction enzymes, R.PabI, is not an endonuclease but a sequence-specific adenine DNA glycosylase. The structure of the R.PabI-DNA complex shows that R.PabI unwinds DNA at a 5'-GTAC-3' site and flips the guanine and adenine bases out of the DNA helix to recognize the sequence. R.PabI catalyses the hydrolysis of the N-glycosidic bond between the adenine base and the sugar in the DNA and produces two opposing apurinic/apyrimidinic (AP) sites. The opposing AP sites are cleaved by heat-promoted β elimination and/or by endogenous AP endonucleases of host cells to introduce a double-strand break.
    Nature Communications 01/2014; 5:3178. · 10.02 Impact Factor
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    Iwona Mruk, Ichizo Kobayashi
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    ABSTRACT: One of the simplest classes of genes involved in programmed death is that containing the toxin-antitoxin (TA) systems of prokaryotes. These systems are composed of an intracellular toxin and an antitoxin that neutralizes its effect. These systems, now classified into five types, were initially discovered because some of them allow the stable maintenance of mobile genetic elements in a microbial population through postsegregational killing or the death of cells that have lost these systems. Here, we demonstrate parallels between some TA systems and restriction-modification systems (RM systems). RM systems are composed of a restriction enzyme (toxin) and a modification enzyme (antitoxin) and limit the genetic flux between lineages with different epigenetic identities, as defined by sequence-specific DNA methylation. The similarities between these systems include their postsegregational killing and their effects on global gene expression. Both require the finely regulated expression of a toxin and antitoxin. The antitoxin (modification enzyme) or linked protein may act as a transcriptional regulator. A regulatory antisense RNA recently identified in an RM system can be compared with those RNAs in TA systems. This review is intended to generalize the concept of TA systems in studies of stress responses, programmed death, genetic conflict and epigenetics.
    Nucleic Acids Research 08/2013; · 8.81 Impact Factor
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    ABSTRACT: Identifying population structure forms an important basis for genetic and evolutionary studies. Most current methods to identify population structure have limitations in analyzing haplotypes and recombination across the genome. Recently, a method of chromosome painting in silico has been developed to overcome these shortcomings and has been applied to multiple human genome sequences. This method detects the genome-wide transfer of DNA sequence chunks through homologous recombination. Here, we apply it to the frequently recombining bacterial species Helicobacter pylori, which has infected Homo sapiens since their birth in Africa and shows wide phylogeographic divergence. Multiple complete genome sequences were analyzed including sequences from Okinawa, Japan, that we recently sequenced. The newer method revealed a finer population structure than revealed by a previous method that examines only MLST housekeeping genes or a phylogenetic network analysis of the core genome. Novel subgroups were found in Europe, Amerind and East Asia groups. Examination of genetic flux showed some singleton strains to be hybrids of subgroups and revealed evident signs of population admixture in Africa, Europe, and parts of Asia. We expect this approach to further our understanding of intraspecific bacterial evolution by revealing population structure at a finer scale.
    Molecular Biology and Evolution 03/2013; · 10.35 Impact Factor
  • Yoshikazu Furuta, Ichizo Kobayashi
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    ABSTRACT: Transfer of mobile genetic elements between prokaryotes is limited by restriction‑modification systems. Restriction‑modification systems consist of a modification enzyme that epigenetically methylates a specific DNA sequence, and a restriction endonuclease (restriction enzyme) that cuts DNA lacking this epigenetic mark. These elements were discovered because they attack mobile genetic elements. However, recent studies have revealed that they are themselves mobile. In some cases, the mobility of restriction‑modification systems is through symbiosis with other forms of mobile elements. In other cases, movement is unlinked to other mobile elements. The systems may insert into the genome with long and variable target duplication, or into the intergenic region of an operon. Insertion of restriction‑modification systems induces other genome rearrangements such as amplification and inversion. Even a domain within a protein can be the unit of mobility: some restriction‑modification system subunits that recognize a target DNA sequence contain mobile amino acid sequences that can apparently move between different domains of a protein through recombination of DNA sequences encoding them. This mobility extends the biological significance of restriction‑modification systems beyond defense: the systems define, and sometimes even force, epigenetic order on a genome. The multilevel conflicts involving these mobile epigenetic elements may drive prokaryotic evolution.
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    Yoshikazu Furuta, Ichizo Kobayashi
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    ABSTRACT: DNA methylation is one of the best studied epigenetic modifications observed in prokaryotes as well as eukaryotes. It affects nearby gene expression. Most DNA methylation reactions in prokaryotes are catalyzed by a DNA methyltransferase, the modification enzyme of a restriction-modification (RM) system. Its target recognition domain (TRD) recognizes a specific DNA sequence for methylation. In this commentary, we review recent evidence for movement of TRDs between non-orthologous genes and movement within a gene. These movements are likely mediated by DNA recombination machinery, and are expected to alter the methylation status of a genome. Such alterations potentially lead to changes in global gene expression pattern and various phenotypes. The targets of natural selection in adaptive evolution might be these diverse methylomes rather than diverse genome sequences, the target according to the current paradigm in biology. This "epigenetics-driven adaptive evolution" hypothesis can explain several observations in the evolution of prokaryotes and eukaryotes.
    Mobile genetic elements. 11/2012; 2(6):292-296.
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    Yoshikazu Furuta, Ichizo Kobayashi
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    ABSTRACT: Comparisons of proteins show that they evolve through the movement of domains. However, in many cases, the underlying mechanisms remain unclear. Here, we observed the movements of DNA recognition domains between non-orthologous proteins within a prokaryote genome. Restriction-modification (RM) systems, consisting of a sequence-specific DNA methyltransferase and a restriction enzyme, contribute to maintenance/evolution of genomes/epigenomes. RM systems limit horizontal gene transfer but are themselves mobile. We compared Type III RM systems in Helicobacter pylori genomes and found that target recognition domain (TRD) sequences are mobile, moving between different orthologous groups that occupy unique chromosomal locations. Sequence comparisons suggested that a likely underlying mechanism is movement through homologous recombination of similar DNA sequences that encode amino acid sequence motifs that are conserved among Type III DNA methyltransferases. Consistent with this movement, incongruence was observed between the phylogenetic trees of TRD regions and other regions in proteins. Horizontal acquisition of diverse TRD sequences was suggested by detection of homologs in other Helicobacter species and distantly related bacterial species. One of these RM systems in H. pylori was inactivated by insertion of another RM system that likely transferred from an oral bacterium. TRD movement represents a novel route for diversification of DNA-interacting proteins.
    Nucleic Acids Research 07/2012; 40(18):9218-32. · 8.81 Impact Factor
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    ABSTRACT: The RecBCD enzyme is important for both restriction of foreign DNA and recombinational DNA repair. Switching enzyme function from the destructive antiviral state to the productive recombinational state is regulated by the recombination hotspot, χ (5'-GCTGGTGG-3'). Recognition of χ is unique in that it is recognized as a specific sequence within single-stranded DNA (ssDNA) during DNA translocation and unwinding by RecBCD. The molecular determinants of χ recognition and the subsequent alteration in function are unknown. Consequently, we mutated residues within the RecC subunit that comprise a channel where ssDNA is thought to be scanned for a χ sequence. These mutants were characterized in vivo with regard to χ recognition, UV-sensitivity, phage degradation, and recombination proficiency. Of 38 residues mutated, 11 were previously undescribed mutations that altered χ recognition. The mutants fell into two classes: five that failed to respond to χ, and six that suggested a relaxed specificity for χ recognition. The location of the first set of mutations defines a recognition structure responsible for sequence-specific binding of ssDNA. The second set defines a highly conserved structure, linked to the recognition structure, which we hypothesize regulates conversion of RecBCD from a molecular machine that destroys DNA to one that repairs it. These findings offer insight into the evolution of enzymes with alternate χ recognition specificities.
    Proceedings of the National Academy of Sciences 05/2012; 109(23):8901-6. · 9.81 Impact Factor
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    ABSTRACT: The nature of a species remains a fundamental and controversial question. The era of genome/metagenome sequencing has intensified the debate in prokaryotes because of extensive horizontal gene transfer. In this study, we conducted a genome-wide survey of outcrossing homologous recombination in the highly sexual bacterial species Helicobacter pylori. We conducted multiple genome alignment and analyzed the entire data set of one-to-one orthologous genes for its global strains. We detected mosaic structures due to repeated recombination events and discordant phylogenies throughout the genomes of this species. Most of these genes including the "core" set of genes and horizontally transferred genes showed at least one recombination event. Taking into account the relationship between the nucleotide diversity and the minimum number of recombination events per nucleotide, we evaluated the recombination rate in every gene. The rate appears constant across the genome, but genes with a particularly high or low recombination rate were detected. Interestingly, genes with high recombination included those for DNA transformation and for basic cellular functions, such as biosynthesis and metabolism. Several highly divergent genes with a high recombination rate included those for host interaction, such as outer membrane proteins and lipopolysaccharide synthesis. These results provide a global picture of genome-wide distribution of outcrossing homologous recombination in a bacterial species for the first time, to our knowledge, and illustrate how a species can be shaped by mutual homologous recombination.
    Genome Biology and Evolution 04/2012; 4(5):628-40. · 4.76 Impact Factor
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    Kyungtaek Lim, Yoshikazu Furuta, Ichizo Kobayashi
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    ABSTRACT: Ribosomal RNA (rRNA) genes, essential to all forms of life, have been viewed as highly conserved and evolutionarily stable, partly because very little is known about their natural variations. Here, we explored large-scale variations of rRNA genes through bioinformatic analyses of available complete bacterial genomic sequences with an emphasis on formation mechanisms and biological significance. Interestingly, we found bacterial genomes in which no 16S rRNA genes harbor the conserved core of the anti-Shine-Dalgarno sequence (5'-CCTCC-3'). This loss was accompanied by elimination of Shine-Dalgarno-like sequences upstream of their protein-coding genes. Those genomes belong to 1 or 2 of the following categories: primary symbionts, hemotropic Mycoplasma, and Flavobacteria. We also found many rearranged rRNA genes and reconstructed their history. Conjecturing the underlying mechanisms, such as inversion, partial duplication, transposon insertion, deletion, and substitution, we were able to infer their biological significance, such as co-orientation of rRNA transcription and chromosomal replication, lateral transfer of rRNA gene segments, and spread of rRNA genes with an apparent structural defect through gene conversion. These results open the way to understanding dynamic evolutionary changes of rRNA genes and the translational machinery.
    Molecular Biology and Evolution 03/2012; 29(10):2937-48. · 10.35 Impact Factor
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    Genome biology 01/2012; 12(11):412. · 10.30 Impact Factor
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    Masaki Fukuyo, Akira Sasaki, Ichizo Kobayashi
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    ABSTRACT: Pathogen infection often leads to the expression of virulence and host death when the host-pathogen symbiosis seems more beneficial for the pathogen. Previously proposed explanations have focused on the pathogen's side. In this work, we tested a hypothesis focused on the host strategy. If a member of a host population dies immediately upon infection aborting pathogen reproduction, it can protect the host population from secondary infections. We tested this "Suicidal Defense Against Infection" (SDAI) hypothesis by developing an experimental infection system that involves a huge number of bacteria as hosts and their virus as pathogen, which is linked to modeling and simulation. Our experiments and simulations demonstrate that a population with SDAI strategy is successful in the presence of spatial structure but fails in its absence. The infection results in emergence of pathogen mutants not inducing the host suicide in addition to host mutants resistant to the pathogen.
    Scientific Reports 01/2012; 2:238. · 5.08 Impact Factor
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    ABSTRACT: Epigenetic DNA methylation is involved in many biological processes. An epigenetic status can be altered by gain or loss of a DNA methyltransferase gene or its activity. Repair of DNA damage can also remove DNA methylation. In response to such alterations, DNA endonucleases that sense DNA methylation can act and may cause cell death. Here, we explored the possibility that McrBC, a methylation-dependent DNase of Escherichia coli, cleaves DNA at a replication fork. First, we found that in vivo restriction by McrBC of bacteriophage carrying a foreign DNA methyltransferase gene is increased in the absence of homologous recombination. This suggests that some cleavage events are repaired by recombination and must take place during or after replication. Next, we demonstrated that the enzyme can cleave a model DNA replication fork in vitro. Cleavage of a fork required methylation on both arms and removed one, the other or both of the arms. Most cleavage events removed the methylated sites from the fork. This result suggests that acquisition of even rarely occurring modification patterns will be recognized and rejected efficiently by modification-dependent restriction systems that recognize two sites. This process might serve to maintain an epigenetic status along the genome through programmed cell death.
    Nucleic Acids Research 03/2011; 39(13):5489-98. · 8.81 Impact Factor
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    Iwona Mruk, Yaoping Liu, Liying Ge, Ichizo Kobayashi
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    ABSTRACT: Restriction-modification systems consist of a modification enzyme that methylates a specific DNA sequence and a restriction endonuclease that cleaves DNA lacking this epigenetic signature. Their gene expression should be finely regulated because their potential to attack the host bacterial genome needs to be controlled. In the EcoRI system, where the restriction gene is located upstream of the modification gene in the same orientation, we previously identified intragenic reverse promoters affecting gene expression. In the present work, we identified a small (88 nt) antisense RNA (Rna0) transcribed from a reverse promoter (P(REV0)) at the 3' end of the restriction gene. Its antisense transcription, as measured by transcriptional gene fusion, appeared to be terminated by the P(M1,M2) promoter. P(M1,M2) promoter-initiated transcription, in turn, appeared to be inhibited by P(REV0). Mutational inactivation of P(REV0) increased expression of the restriction gene. The biological significance of this antisense transcription is 2-fold. First, a mutation in P(REV0) increased restriction of incoming DNA. Second, the presence of the antisense RNA gene (ecoRIA) in trans alleviated cell killing after loss of the EcoRI plasmid (post-segregational killing). Taken together, these results strongly suggested the involvement of an antisense RNA in the biological regulation of this restriction-modification system.
    Nucleic Acids Research 03/2011; 39(13):5622-32. · 8.81 Impact Factor
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    ABSTRACT: The genome of Helicobacter pylori, an oncogenic bacterium in the human stomach, rapidly evolves and shows wide geographical divergence. The high incidence of stomach cancer in East Asia might be related to bacterial genotype. We used newly developed comparative methods to follow the evolution of East Asian H. pylori genomes using 20 complete genome sequences from Japanese, Korean, Amerind, European, and West African strains. A phylogenetic tree of concatenated well-defined core genes supported divergence of the East Asian lineage (hspEAsia; Japanese and Korean) from the European lineage ancestor, and then from the Amerind lineage ancestor. Phylogenetic profiling revealed a large difference in the repertoire of outer membrane proteins (including oipA, hopMN, babABC, sabAB and vacA-2) through gene loss, gain, and mutation. All known functions associated with molybdenum, a rare element essential to nearly all organisms that catalyzes two-electron-transfer oxidation-reduction reactions, appeared to be inactivated. Two pathways linking acetyl~CoA and acetate appeared intact in some Japanese strains. Phylogenetic analysis revealed greater divergence between the East Asian (hspEAsia) and the European (hpEurope) genomes in proteins in host interaction, specifically virulence factors (tipα), outer membrane proteins, and lipopolysaccharide synthesis (human Lewis antigen mimicry) enzymes. Divergence was also seen in proteins in electron transfer and translation fidelity (miaA, tilS), a DNA recombinase/exonuclease that recognizes genome identity (addA), and DNA/RNA hybrid nucleases (rnhAB). Positively selected amino acid changes between hspEAsia and hpEurope were mapped to products of cagA, vacA, homC (outer membrane protein), sotB (sugar transport), and a translation fidelity factor (miaA). Large divergence was seen in genes related to antibiotics: frxA (metronidazole resistance), def (peptide deformylase, drug target), and ftsA (actin-like, drug target). These results demonstrate dramatic genome evolution within a species, especially in likely host interaction genes. The East Asian strains appear to differ greatly from the European strains in electron transfer and redox reactions. These findings also suggest a model of adaptive evolution through proteome diversification and selection through modulation of translational fidelity. The results define H. pylori East Asian lineages and provide essential information for understanding their pathogenesis and designing drugs and therapies that target them.
    BMC Microbiology 01/2011; 11:104. · 2.98 Impact Factor
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    ABSTRACT: A protein function is carried out by a specific domain localized at a specific position. In the present study, we report that, within a gene, a specific amino acid sequence can move between a certain position and another position. This was discovered when the sequences of restriction-modification systems within the bacterial species Helicobacter pylori were compared. In the specificity subunit of Type I restriction-modification systems, DNA sequence recognition is mediated by target recognition domain 1 (TRD1) and TRD2. To our surprise, several sequences are shared by TRD1 and TRD2 of genes (alleles) at the same locus (chromosomal location); these domains appear to have moved between the two positions. The gene/protein organization can be represented as x-(TRD1)-y-x-(TRD2)-y, where x and y represent repeat sequences. Movement probably occurs by recombination at these flanking DNA repeats. In accordance with this hypothesis, recombination at these repeats also appears to decrease two TRDs into one TRD or increase these two TRDs to three TRDs (TRD1-TRD2-TRD2) and to allow TRD movement between genes even at different loci. Similar movement of domains between TRD1 and TRD2 was observed for the specificity subunit of a Type IIG restriction enzyme. Similar movement of domain between TRD1 and TRD2 was observed for Type I restriction-modification enzyme specificity genes in two more eubacterial species, Streptococcus pyogenes and Mycoplasma agalactiae. Lateral domain movements within a protein, which we have designated DOMO (domain movement), represent novel routes for the diversification of proteins.
    PLoS ONE 01/2011; 6(4):e18819. · 3.53 Impact Factor
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    ABSTRACT: Helicobacter pylori is a gastric pathogen that infects half the human population and causes gastritis, ulcers, and cancer. The cagA gene product is a major virulence factor associated with gastric cancer. It is injected into epithelial cells, undergoes phosphorylation by host cell kinases, and perturbs host signaling pathways. CagA is known for its geographical, structural, and functional diversity in the C-terminal half, where an EPIYA host-interacting motif is repeated. The Western version of CagA carries the EPIYA segment types A, B, and C, while the East Asian CagA carries types A, B, and D and shows higher virulence. Many structural variants such as duplications and deletions are reported. In this study, we gained insight into the relationships of CagA variants through various modes of recombination, by analyzing all known cagA variants at the DNA sequence level with the single nucleotide resolution. Processes that occurred were: (i) homologous recombination between DNA sequences for CagA multimerization (CM) sequence; (ii) recombination between DNA sequences for the EPIYA motif; and (iii) recombination between short similar DNA sequences. The left half of the EPIYA-D segment characteristic of East Asian CagA was derived from Western type EPIYA, with Amerind type EPIYA as the intermediate, through rearrangements of specific sequences within the gene. Adaptive amino acid changes were detected in the variable region as well as in the conserved region at sites to which no specific function has yet been assigned. Each showed a unique evolutionary distribution. These results clarify recombination-mediated routes of cagA evolution and provide a solid basis for a deeper understanding of its function in pathogenesis.
    PLoS ONE 01/2011; 6(8):e23499. · 3.53 Impact Factor
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    ABSTRACT: The birth and death of genes is central to adaptive evolution, yet the underlying genome dynamics remain elusive. The availability of closely related complete genome sequences helps to follow changes in gene contents and clarify their relationship to overall genome organization. Helicobacter pylori, bacteria in our stomach, are known for their extreme genome plasticity through mutation and recombination and will make a good target for such an analysis. In comparing their complete genome sequences, we found that gain and loss of genes (loci) for outer membrane proteins, which mediate host interaction, occurred at breakpoints of chromosomal inversions. Sequence comparison there revealed a unique mechanism of DNA duplication: DNA duplication associated with inversion. In this process, a DNA segment at one chromosomal locus is copied and inserted, in an inverted orientation, into a distant locus on the same chromosome, while the entire region between these two loci is also inverted. Recognition of this and three more inversion modes, which occur through reciprocal recombination between long or short sequence similarity or adjacent to a mobile element, allowed reconstruction of synteny evolution through inversion events in this species. These results will guide the interpretation of extensive DNA sequencing results for understanding long- and short-term genome evolution in various organisms and in cancer cells.
    Proceedings of the National Academy of Sciences 01/2011; 108(4):1501-6. · 9.81 Impact Factor
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    ABSTRACT: Potential mobility of restriction-modification systems has been suggested by evolutionary/bioinformatic analysis of prokaryotic genomes. Here we demonstrate in vivo movement of a restriction-modification system within a genome under a laboratory condition. After blocking replication of a temperature-sensitive plasmid carrying a PaeR7I restriction-modification system in Escherichia coli cells, the plasmid was found integrated into the chromosome of the surviving cells. Sequence analysis revealed that, in the majority of products, the restriction-modification system was linked to chromosomal insertion sequences (ISs). Three types of products were: (I) apparent co-integration of the plasmid and the chromosome at a chromosomal IS1 or IS5 copy (24/28 analyzed); (II) de novo insertion of IS1 with the entire plasmid except for a 1-3 bp terminal deletion (2/28); and (III) reciprocal crossing-over between the plasmid and the chromosome involving 1-3 bp of sequence identity (2/28). An R-negative mutation apparently decreased the efficiency of successful integration by two orders of magnitude. Reconstruction experiments demonstrated that the restriction-dependence was mainly due to selection against cells without proper integration: their growth was inhibited by the restriction enzyme action. These results demonstrate collaboration of a mobile element and a restriction-modification system for successful joint migration. This collaboration may have promoted the spread and, therefore, the long-term persistence of these complexes and restriction-modification systems in a wide range of prokaryotes.
    PLoS ONE 01/2011; 6(1):e16554. · 3.53 Impact Factor

Publication Stats

3k Citations
539.48 Total Impact Points

Institutions

  • 1988–2014
    • The University of Tokyo
      • • Department of Applied Biological Chemistry
      • • Department of Medical Genome Sciences
      • • Graduate School of Frontier Sciences
      • • Institute of Medical Science
      • • Department of Molecular Cell Biology
      • • School of Medicine
      Edo, Tōkyō, Japan
  • 2011–2013
    • University of Gdansk
      • Department of Microbiology
      Gdańsk, Pomeranian Voivodeship, Poland
  • 2009–2012
    • Kurume University
      • Graduate School of Medicine
      Куруме, Fukuoka, Japan
  • 2000–2010
    • Keio University
      • Department of Applied Physics and Physico-Informatics
      Edo, Tōkyō, Japan
  • 2006
    • National Institute for Basic Biology
      Okazaki, Aichi, Japan
  • 1998
    • Stanford University
      Palo Alto, California, United States