Evolution of the Adh locus in the Drosophila willistoni group: the loss of an intron, and shift in codon usage

We report here the DNA sequence of the alcohol dehydrogenase gene (Adh)cloned from Drosophila willistoni. The three major findings are as follows:(1) Relative to all other Adh genes known from Drosophila, D. willistoniAdh has the last intron precisely deleted; PCR directly from total genomicDNA indicates that the deletion exists in all members of the willistonigroup but not in any other group, including the closely related saltansgroup. Otherwise the structure and predicted protein are very similar tothose of other species. (2) There is a significant shift in codon usage,especially compared with that in D. melanogaster Adh. The most strikingshift is from C to U in the wobble position (both third and firstposition). Unlike the codon-usage-bias pattern typical of highly biasedgenes in D. melanogaster, including Adh, D. willistoni has nearly 50% G + Cin the third position. (3) The phylogenetic information provided by thisnew sequence is in agreement with almost all other molecular andmorphological data, in placing the obscura group closer to the melanogastergroup, with the willistoni group farther distant but still clearly withinthe subgenus Sophophora.