Duplication, dicistronic transcription, and subsequent evolution of the Alcohol dehydrogenase and Alcohol dehydrogenase-related genes in drosophila

It has recently been discovered that the Alcohol dehydrogenase and Alcohol dehydrogenase-related genes of Drosophila melanogaster and closely related species constitute a single transcription unit and that the Alcohol dehyldr ogennse-related gene is exclusively expressed from a dicistronic mRNA. Here , we show that in Drosophila lebnnanensis, subgenus Scaptodrosophila, Adhr is also transcribed as a dicistronic transcript with Adh. Using degenerate primers designed on the sequence of the known ADHR proteins, we have been a ble to amplify and sequence a partial sequence of Adhr in species represent ative of the whole subgenus Drosophila. This has allowed the study of the o rganization and expression of Adhr in Drosophila buzzatii. We find that in D. buzzatii Adhr is transcribed as a monocistronic transcript. Adh and Adhr are believed to originate by duplication, and our data suggest that the co transcription of these two genes was the primitive state, and that their in dependent transcription in the subgenus Drosophila is derived. We can ratio nalize the D. buzzatii condition as bring correlated with the two genes evo lving independent transcriptional control. However, why these two genes wit h clear divergence in the functions of their proteins should remain cotrans cribed in groups as divergent as the subgenus Sophophora and the subgenus S captodrosophila remains a mystery.