Transcription at the ecdysone-inducible locus 2B5 in Drosophila.

The Broad-Complex (BR-C) of D. melanogaster, mapping at the 2B5 early ecdysone puff, mediates ecdysone-induced processes. We present here the transcriptional analysis of the locus in both wild type and representative mutants. Two well defined regions are transcribed, only one of which has a pattern consistent with the proposed 2B5 located BR-C function. The 2B5 region is actively transcribed in early third instar larvae before ecdysone levels increase. Ecdysone switches this early pattern to a complex late type which requires the presence of functional BR-C product. Therefore, BR-C self-regulates its own ecdysone-induced transcription. The effect of 2B5 mutations on transcription at several intermolt, early and late puffs is also described. Null mutations at the 2B5 locus prevents ecdysone inducible transcription. This evidence supports the fact that 2B5 codes for an ecdysone-dependent transcriptional regulator.