MOLECULAR EVOLUTION OF THE 5'-FLANKING REGIONS OF THE DUPLICATED AMY GENES IN DROSOPHILA-MELANOGASTER SPECIES SUBGROUP

The nucleotide sequences of the 5'-flanking regions of the duplicated Amy genes in eight sibling species belonging to the melanogaster speci es subgroup are analyzed. In Drosophila melanogaster, a region of abou t 450 bp immediately upstream of the translation initiation site of th e two paralogous genes (the proximal and distal genes) has sequence si milarities. However, we could not detect any significant sequence simi larity in the region mon upstream than -450. This result indicates tha t the coding regions of the ancestral Amy gene were duplicated togethe r with 450 bp of the 5'-flanking region as one unit. Multiple alignmen t of these 450-bp sequences in the proximal and distal genes of all ei ght species revealed a mosaic pattern of highly conserved and divergen t regions. The conserved regions included almost all the putative regu latory elements identified in previous analyses of the sequences. A ph ylogenetic analysis of the aligned sequences shows that these 450-bp s equences are clustered into the proximal and the distal groups. As a w hole, the divergence between groups in this region is very large in co ntrast to that in the coding regions. Based on the divergence between groups, the 450-bp region is divided into two subregions. We found tha t the ratios of the divergence between groups to that within groups di ffer in the two subregions. From these observations, we discuss a poss ibility of positive selection acting on the subregion immediately upst ream of the Amy coding region to cause divergence of regulatory elemen ts of the paralogous genes.