Sequence analysis of the indirect flight muscle actin-encoding gene of Drosophila simulans

A genomic clone of the Drosophila simulans indirect flight muscle actin-encoding gene (Act88F) has been isolated, and the sequence of a 3358-nucleotide segment corresponding to the Drosophila melanogaster Act88F transcription unit is presented. The ACt88F homologs in these two sibling species encode identical proteins and the general genomic organization of the Act88F locus is highly conserved, including the location of the transcription start point, and the size and position of intron/exon junctions. Substitutions within the 5' flanking region, however, are clearly nonuniform and the regions of lowest divergence coincide with regions that have been implicated in transcript accumulation and the regulation of tissue-specific expression. Silent substitutions within the coding regions have been compared to five other gene homologs in these sibling species. The rate of silent substitution at these loci varies more than threefold, suggesting selection at the codon level.