Partial characterization and evolution of Adh-Adhr in Drosophila dunni.

We sequenced 2123 bp of the Adh-Adhr genomic region of Drosophila dunni of the cardini group from two cloned DNA PCR fragments and from two cDNA clones of an Adh transcript. This comprises the Adh coding region and introns, 3' UTR, intergenic sequence, and most of Adhr, which is 260 bp downstream of Adh. Both genes have the typical Drosophila melanogaster Adh structure of three exons and two introns, except for changes in the putative 8 bp sequence involved in downregulation within the 3' UTR of Adh. Two amino acid substitutions could explain the low activity previously reported for this enzyme in D. dunni: Thr --> Lys at position 191 and Val --> Thr at position 189. D. dunni's Adh has the lowest codon bias reported so far for Drosophila species, and based on analysis of the nucleotide substitution rate, it is less conserved than Adhr.