Regulation of tissue-specific expression of the esterase S gene in Drosophila virilis

The esterase S gene (estS) of Drosophila virilis is specifically expressed in the ejaculatory bulbs of males. Its sequencing shows similarities between estS product and other esterases of different origin. The transcription of estS in ejaculatory bulbs is at least 2 orders of magnitude higher than in other tissues of males. Two promoters, P1 (distal) and P2 (proximal), and two different transcripts were identified. The promoter P2 is used much more efficiently, and in a stringent, tissue-specific manner. The transcription from P1 takes place in different tissues and stages of development of D. virilis. However, the mRNA transcribed from P1 seems to be inactive in translation as there are three open-reading frames (ORF) between P1 and P2, which may block the translation in P1 initiated mRNA. Insertion of sequence containing the three ORFs into the 5' untranslated region of the CAT gene strongly inhibited expression of CAT. Point mutations destroying the three ORFs completely eliminate the inhibitory effect. Hence tissue-specific expression of the estS gene may depend on control at the level of transcription, promoter selection and translation.