A cis-acting regulator of enzyme tissue specificity in Drosophila is expressed at the RNA level.

Alcohol dehydrogenase (ADH) is expressed according to qualitatively different patterns in Drosophila grimshawi and two closely related species, D. orthofascia and D. formella. This regulatory difference is under control of a cis-acting genetic factor. The ADH of these species is very similar to ADH of D. melanogaster and a genomic ADH clone derived from the latter hybridizes specifically to ADH coding sequences of the other species. Using this hybridization probe, it is shown that the above cis-acting regulator acts before or shortly after transcription to control ADH expression.