NUCLEOTIDE VARIATION AND CONSERVATION AT THE DPP LOCUS, A GENE CONTROLLING EARLY DEVELOPMENT IN DROSOPHILA

A study of polymorphism and species divegence of the dpp gene of Droso phila has been made. Eighteen lines from a population of D. melanogast er were sequenced for 5200 bp of the Hin region of the gene, coding fo r the dpp polypeptide. A comparison was made with sequence from D. sim ulans. Ninety-six silent polymorphisms and three amino acid replacemen t polymorphisms were found. The overall silent polymorphism (0.0247) i s low, but haplotype diversity (0.0066 for effectively silent sites an d 0.0054 for all sites) is in the range found for enzyme loci. Amino a cid variation is absent in the N-terminal signal peptide, the C-termin al TGF-beta peptide and in the N-terminal half of the pro-protein regi on. At the nucleotide level there is strong conservation in the middle half of the large intron and in the 3' untranslated sequence of the l ast exon. The 3' untranslated conservation, which is perfect for 110 b p among all the divergent species, is unexplained. There is strong pos itive linkage disequilibrium among polymorphic sites, with stretches o f apparent gene conversion among originally divergent sequences. The p opulation apparently is a migration mixture of divergent clades.