GROUCHO IS REQUIRED FOR DROSOPHILA NEUROGENESIS, SEGMENTATION, AND SEX DETERMINATION AND INTERACTS DIRECTLY WITH HAIRY-RELATED BHLH PROTEINS

We have used the interaction trap, a yeast two-hybrid system, to ident ify proteins interacting with hairy, a basic-helix-loop-helix (bHLH) p rotein that represses transcription during Drosophila embryonic segmen tation. We find that the groucho (gro) protein binds specifically to h airy and also to hairy-related bHLH proteins encoded by deadpan and th e Enhancer of split complex. The C-terminal WRPW motif present in all these bHLH proteins is essential for this interaction. We demonstrate that these associations reflect in vivo maternal requirements for gro during neurogenesis, segmentation, and sex determination, three proces ses regulated by the above bHLH proteins, and we propose that gro is a transcriptional corepressor recruited to specific target promoters by hairy-related bHLH proteins.