Comparison of regions coding for tRNA(His) genes of mitochondrial and chloroplast DNA in sunflower: a proposal concerning the classification of 'CP-like' tRNA genes.
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Biomedical subjects
Publications and source records attributed to R Gallerani.
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The gene encoding subunit III of cytochrome oxidase (COXIII) has been identified in the sunflower mitochondrial genome. The COXIII coding region is located 570 bp downstream of a 477 bp open reading frame (ORFB). Sequence comparisons and hybridization experiments show that ORFB sequences are conserved in other plant mitochondrial genomes. Nucleotide and amino acid sequence comparisons suggest that RNA editing is required in sunflower mitochondria to synthesize a functional COXIII polypeptide.
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The base sequence of large part of the mitochondrial DNA of Wistar rats is presented. The sequence is compared with those of other mammalian mitochondrial DNAs. The nucleotide and amino acid homologies, codon strategy, nature and patterns of substitutions are reported. It results a very high amount of silent substitutions and, in short divergence time, a predominance of transitions on transversions. In both types of substitutions a strong bias in avoiding the use of the G in the third codon position is observed.
We have determined the nucleotide sequences of thirteen rat mt tRNA genes. The features of the primary and secondary structures of these tRNAs show that those for Gln, Ser, and f-Met resemble, while those for Lys, Cys, and Trp depart strikingly from the universal type. The remainder are slightly abnormal. Among many mammalian mt DNA sequences, those of mt tRNA genes are highly conserved, thus suggesting for those genes an additional, perhaps regulatory, function. A simple evolutionary relationship between the tRNAs of animal mitochondria and those of eukaryotic cytoplasm, of lower eukaryotic mitochondria or of prokaryotes, is not evident owing to the extreme divergence of the tRNA sequences in the two groups. However, a slightly higher homology does exist between a few animal mt tRNAs and those from prokaryotes or from lower eukaryotic mitochondria.
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We have sequenced the Eco R(1) fragment D from rat mitochondrial DNA. It contains one third of the tRNA (Val) gene (the remaining part has been sequenced from the 3' end of the Eco R(1) fragment A) the complete gene for the large mt 16S rRNA, the tRNA (Leu) gene and the 5' end of an unidentified reading frame. The mt gene for the large rRNA from rat has been aligned with the homologous genes from mouse and human using graphic computer programs. Hypervariable regions at the center of the molecule and highly conserved regions toward the 3' end have been detected. The mt gene for tRNA Leu is of the conventional type and its primary structure is highly conserved among mammals. The mt gene for tRNA(Val) shows characteristics similar to those of other mt tRNA genes but the degree of homology is lower. Comparative studies confirm that AGA and AGG are read as stop codons in mammalian mitochondria.
The base sequence of the Eco-RI D fragment from rat liver mtDNA, cloned in recombinant plasmid, has been analyzed, This fragment contains the genes for the 16SRNA of the large ribosomal subunit and the tRNA(Leu). Comparisons between these genes and corresponding regions either in other mitochondrial genomes or in E. coli DNA are presented, that allow some interesting evolutionary and phylogenetic considerations.
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