Genes for cytochrome c oxidase subunit I, URF2, and three tRNAs in Drosophila mitochondrial DNA.

Genes for URF2, tRNAtrp, tRNAcys, tRNAtyr and cytochrome c oxidase subunit I (COI) have been identified within a sequenced segment of the Drosophila yakuba mtDNA molecule. The five genes are arranged in the order given. Transcription of the tRNAcys and tRNAtyr genes is in the same direction as replication, while transcription of the URF2, tRNAtrp and COI genes is in the opposite direction. A similar arrangement of these genes is found in mammalian mtDNA except that in the latter, the tRNAala and tRNAasn genes are located between the tRNAtrp and tRNAcys genes. Also, a sequence found between the tRNAasn and tRNAcys genes in mammalian mtDNA, which is associated with the initiation of second strand DNA synthesis, is not found in this region of the D. yakuba mtDNA molecule. As the D. yakuba COI gene lacks a standard translation initiation codon, we consider the possibility that the quadruplet ATAA may serve this function. As in other D. yakuba mitochondrial polypeptide genes, AGA codons in the URF2 and COI genes do not correspond in position to arginine-specifying codons in the equivalent genes of mouse and yeast mtDNAs, but do most frequently correspond to serine-specifying codons.