Evolution of the autosomal chorion locus in Drosophila. I. General organization of the locus and sequence comparisons of genes s15 and s19 in evolutionary distant species.

We have isolated clones corresponding to the autosomal chorion locus of Drosophila melanogaster, from two distantly (D. virilis and D. grimshawi) and one closely (D. subobscura) related species. In all the species the locus is unique within the genome and encompasses the same four chorion genes and an adjacent nonchorion gene, in the same order. In all species the locus specifically amplifies in the ovary, as in D. melanogaster. We present the nucleotide sequences of DNA segments that total 8.3 kb in length and include gene s15-1 from D. subobscura, D. virilis, and D. grimshawi as well as gene s19-1 from D. subobscura and D. grimshawi. They show clearly nonuniform rates of divergence, both within and outside the limits of the genes. Highlighted by a background of extensive sequence divergence elsewhere in the extragenic region, highly conserved elements are observed in the 5' flanking DNA and might represent regulatory elements.