Nucleotide Sequences within the A + T-rich Region and the Large-rRNA Gene of Mitochondrial DNA Molecules of Drosophila yakuba

Abstract

mtDNA molecules of species of the genus Drosophila contain a region that is distinctly rich in adenine and thymine (A + T). In different species of the melanogaster group, the A + T-rich region ranges in size from 1.0 kb to 5.1 kb, whereas in D. virilis and other species it is about 1.1 kb (for references, see Fauron and Wolstenholme 1980a,b). We have shown that in mtDNA molecules of D. melanogaster, D. simulans, D. mauritiana, D. takahashii, D. yakuba, and D. virilis, the A + T-rich regions (5.1, 4.8, 4.6, 2.5, 1.1, and 1.1 kb, respectively) are homologously located. Using heteroduplex analyses, we have demonstrated that extensive divergences of sequences have occurred in A + T-rich regions of mtDNA molecules, both within species as well as between species (Fauron and Wolstenholme 1980a,b). In all six of the species mentioned above, the origin of replication lies within the A + T-rich region; replication is unidirectional around the molecule as a whole and always occurs in the same direction (Goddard and Wolstenholme 1980). The direction of replication in Drosophila mtDNA is toward the adjacently located rRNA genes, which is opposite to the direction of replication in vertebrate mtDNAs (see Wolstenholme et al. 1979).

RNA transcripts that map in the A + T-rich region have not been detected, and apart from its inclusion of the replication origin, no other function of this region is known (for discussion and references, see Fauron and Wolstenholme 1980b).

We report here the results of sequence studies...