The Drosophila alcohol dehydrogenase gene may have evolved independently of the functionally homologous medfly, olive fly, and flesh fly genes

cDNAs for alcohol dehydrogenase (ADH) isozymes were cloned and sequenced fr om two tephritid fruit flies, the medfly Ceratitis capitata and the olive f ly Bactrocera oleae. Because of the high sequence divergence compared with the Drosophila sequences, the medfly cDNAs were cloned using sequence infor mation from the purified proteins, and the olive fly cDNAs were cloned by f unctional complementation in yeast. The medfly peptide sequences are about 83% identical to each other, and the corresponding mRNAs have the tissue di stribution shown by the corresponding isozymes, ADH-1 and ADH-2. The olive fly peptide sequence is more closely related to medfly ADH-2. The tephritid ADHs share less than 40% sequence identity with Drosophila ADH and ADH-rel ated genes but are >57% identical to the ADH of the flesh fly Sarcophaga pe regrina, a more distantly related species. To explain this unexpected findi ng, it is proposed that the Adh genes of the family Drosophilidae may not b e orthologous to the Adh genes of the other two families, Tephritidae and S arcophagidae.