EVOLUTION OF THE MITOCHONDRIAL ATPASE 6 GENE IN DROSOPHILA - UNUSUALLY HIGH-LEVEL OF POLYMORPHISM IN DROSOPHILA-MELANOGASTER

We have determined 1990 bp mitochondrial DNA sequence which extends fr om 3' en of the cytochrome oxidase subunit I (COI) gene to 5' end of t he COIII gene from two sibling species of Drosophila, D. simulans and D. mauritiana. Analyses of the sequences and part of the NADH dehydrog enase subunit 2 gene and the COI gene together with those from D. mela nogaster and D. yakuba revealed that amino-acid substitution rate of t he ATPase 6 gene seems to be higher in some strains of D. melanogaster than in the other species. High level of amino-acid polymorphism in t his gene was observed in D. melanogaster. Synonymous substitution rate is relatively constant in all the genes examined, suggesting that mut ation rate is not higher in the ATPase 6 gene of D. melanogaster. The amino-acid substitutions found specifically in D. melanogaster are at the sites which are not conserved among mammals, yeast and E. coli. Th ese sites of the ATPase 6 gene might lose the selective constraint in D. melanogaster, and the amino-acid substitutions can be explained by neutral mutations and random genetic drift.