Rearrangements of mitochondrial transfer RNA genes in marsupials
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The nucleotide sequences of the mitochondrial origin of light-strand replication and the five tRNA genes surrounding it were determined for three marsupials. The region was found to be rearranged, leaving only the tRNATyr gene at the same position as in placental mammals andXenopus. Distribution of the same rearranged genotype among two marsupial families indicates that the events causing the rearrangements took place in an early marsupial ancestor. The putative mitochondrial light-strand origin of replication in marsupials contains a hairpin structure similar to other vertebrate origins and, in addition, extensive flanking sequences that are not found in other vertebrates. Sequence comparisons among the marsupials as well as placentals indicate that the tRNATyr gene has been evolving under more constraints than the other tRNA genes.
Key wordsMitochondrial DNA Marsupials tRNA genes Genome organization Evolutionary constraints
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