EVOLUTION OF THE NONCODING REGIONS IN DROSOPHILA MITOCHONDRIAL-DNA - 2 INTERGENIC REGIONS

The sequences of the mitochondrial DNA (mtDNA) segment containing the two intergenic regions were determined for six species belonging to th e Drosophila immigrans species group and compared to the corresponding segments of Drosophila species which had been studied previously. We found remarkable differences in the evolutionary rates of the two inte rgenic regions. The Intergenic I region, which lies between the tRNA(g ln) and the tRNA(ile) genes, was found to be highly conserved in terms of both size (30 ntp) and nucleotide sequence among the species studi ed. In contrast, the sequences of the Intergenic II region, which lies between the tRNA(f-met) and the tRNA(ile) genes, showed considerable variation. The size of rite Intergenic II region ranged from 0 to 88 n tp, and accurate alignment was possible only among sequences from geog raphical strains or very closely related species in the nasuta species subgroup. The observed differences in conservation of the two mtDNA i ntergenic regions ave discussed in light of functional constraints on mtDNA sequences.