The DNA puff gene BhC4-1 of Bradysia hygida is specifically transcribed inearly prepupal salivary glands of Drosophila melanogaster

The BhC4-1 gene of the sciarid Bradysia hygida is located at DNA puff C4 an d is amplified and actively transcribed in the salivary gland at the end of the last larval instar. We show here that a 3.6 kb fragment from the upstr eam region of the BhC4-1 gene is able to drive transcription in transgenic Drosophila specifically in prepupal salivary gland in a temporally regulate d manner. The mRNA is present in maximal amounts in prepupae +3 h; in prepu pae +9 h the levels of BhC4-1 mRNA decline, and it is no longer detected in pupae +24 h. Taken together these results suggest that most, if not all, o f the key promoter regulatory elements were included in the DNA fragments e mployed to transform Drosophila. Moreover, strong expression of the transge nes implies conservation of the regulatory elements involved, since Drosoph ila transcription factors appear to recognize B. hygida regulatory DNA sequ ences. Quantitative Southern blot hybridization indicates that the sequence s from DNA puff C4 are not amplified at detectable levels in salivary gland s of transgenic prepupae when the BhC4-1 gene is transcribed. Transcription of a DNA puff in the absence of amplification indicates that the induction of these processes involves distinct mechanisms.