Mitochondrial genetic code in cestodes.
ABSTRACT The flatworm mitochondrial genetic code, which has been used for all species of the Platyhelminthes, is mainly characterized by AUA codon for isoleucine, AAA codon for asparagine and UAA codon for tyrosine. In eight species of cestodes (Echinococcus multilocularis, Echinococcus granlosus, Taenia solium Taenia saginata, Taenia hydatigena, Taenia crassiceps, Hymenolepis nama and Mesocestoides corti), the cytochrome c oxidase subunit I (COI) genes were partially sequenced to verify this genetic code. Comparison of the COI-encoding nucleotide sequences with those of human, sea urchin, fruit fly, nematode and yeast indicated that the assignments of AUA and AAA codons are adequate for cestodes. In addition, the nucleotide sequences of ATPase subunit 6 (ATP6) gene and its flanking region were compared to examine initiation and stop codons. In the related species of T. solium and T. saginata, the deduced amino acid sequences of ATP6 were homogeneous; however, the conversion of initiation codon AUG into GUG was observed in T. saginata. We also found the similar conversion in T. crassiceps. The C-terminal sequences of putative ATP6 proteins were highly conserved among the eight species and the stop codon UAG was altered to UAA in all Taenia species. The features of the gene-junctional region between NADH dehydrogenase subunit 4 (ND4) and glutamine tRNA (tRNAGln) genes also supported that UAA serves as a stop codon. Based on these results, we propose that the flatworm mitochondrial code should be modified for cestodes, particularly, in an initiating methionine codon (GUG) and a terminating codon (UAA).
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ABSTRACT: The nucleotide sequence of a segment of the mitochondrial DNA (mtDNA) molecule of the liver fluke Fasciola hepatica (phylum Platyhelminthes, class Trematoda) has been determined, within which have been identified the genes for tRNA(ala), tRNA(asp), respiratory chain NADH dehydrogenase subunit I (ND1), tRNA(asn), tRNA(pro), tRNA(ile), tRNA(lys), ND3, tRNA(serAGN), tRNA(trp), and cytochrome c oxidase subunit I (COI). The 11 genes are arranged in the order given and are all transcribed from the same strand of the molecule. The overall order of the F. hepatica mitochondrial genes differs from what is found in other metazoan mtDNAs. All of the sequenced tRNA genes except the one for tRNA(serAGN) can be folded into a secondary structure with four arms resembling most other metazoan mitochondrial tRNAs, rather than the tRNAs that contain a T psi C arm replacement loop, found in nematode mtDNAs. The F. hepatica mitochondrial tRNA(serAGN) gene contains a dihydrouridine arm replacement loop, as is the case in all other metazoan mtDNAs examined to date. AGA and AGG are found in the F. hepatica mitochondrial protein genes and both codons appear to specify serine. These findings concerning F. hepatica mtDNA indicate that both a dihydrouridine arm replacement loop-containing tRNA(serAGN) gene and the use of AGA and AGG codons to specify serine must first have occurred very early in, or before, the evolution of metazoa.Journal of Molecular Evolution 06/1989; 28(5):374-87. · 2.15 Impact Factor
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ABSTRACT: The DNA sequence of the 15,532-base pair (bp) mitochondrial DNA (mtDNA) of the chiton Katharina tunicata has been determined. The 37 genes typical of metazoan mtDNA are present: 13 for protein subunits involved in oxidative phosphorylation, 2 for rRNAs and 22 for tRNAs. The gene arrangement resembles those of arthropods much more than that of another mollusc, the bivalve Mytilus edulis. Most genes abut directly or overlap, and abbreviated stop codons are inferred for four genes. Four junctions between adjacent pairs of protein genes lack intervening tRNA genes; however, at each of these junctions there is a sequence immediately adjacent to the start codon of the downstream gene that is capable of forming a stem-and-loop structure. Analysis of the tRNA gene sequences suggests that the D arm is unpaired in tRNA(ser)(AGN), which is typical of metazoan mtDNAs, and also in tRNA(ser)(UCN), a condition found previously only in nematode mtDNAs. There are two additional sequences in Katharina mtDNA that can be folded into structures resembling tRNAs; whether these are functional genes is unknown. All possible codons except the stop codons TAA and TAG are used in the protein-encoding genes, and Katharina mtDNA appears to use the same variation of the mitochondrial genetic code that is used in Drosophila and Mytilus. Translation initiates at the codons ATG, ATA and GTG. A + T richness appears to have affected codon usage patterns and, perhaps, the amino acid composition of the encoded proteins. A 142-bp non-coding region between tRNA(glu) and CO3 contains a 72-bp tract of alternating A and T.Genetics 11/1994; 138(2):423-43. · 4.39 Impact Factor
Article: Animal mitochondrial genomes.[show abstract] [hide abstract]
ABSTRACT: Animal mitochondrial DNA is a small, extrachromosomal genome, typically approximately 16 kb in size. With few exceptions, all animal mitochondrial genomes contain the same 37 genes: two for rRNAs, 13 for proteins and 22 for tRNAs. The products of these genes, along with RNAs and proteins imported from the cytoplasm, endow mitochondria with their own systems for DNA replication, transcription, mRNA processing and translation of proteins. The study of these genomes as they function in mitochondrial systems-'mitochondrial genomics'-serves as a model for genome evolution. Furthermore, the comparison of animal mitochondrial gene arrangements has become a very powerful means for inferring ancient evolutionary relationships, since rearrangements appear to be unique, generally rare events that are unlikely to arise independently in separate evolutionary lineages. Complete mitochondrial gene arrangements have been published for 58 chordate species and 29 non-chordate species, and partial arrangements for hundreds of other taxa. This review compares and summarizes these gene arrangements and points out some of the questions that may be addressed by comparing mitochondrial systems.Nucleic Acids Research 05/1999; 27(8):1767-80. · 8.28 Impact Factor