A NETWORK OF INTERACTING TRANSCRIPTIONAL REGULATORS INVOLVED IN DROSOPHILA NEURAL FATE SPECIFICATION REVEALED BY THE YEAST 2-HYBRID SYSTEM

Neural fate specification in Drosophila is promoted by the products of the proneural genes, such as those of the achaete-scute complex, and antagonized by the products of the Enhancer of split [E(spl)] complex, hairy, and extramacrochaetae. As all these proteins bear a helix-loop helix (HLH) dimerization domain, we investigated their potential pair wise interactions using the yeast two hybrid system. The fidelity of t he system was established by its ability to closely reproduce the alre ady documented interactions among Da, Ac, Sc, and Extramacrochaetae. W e show that the seven E(spl) basic HLH proteins can form home-and hete rodimers inter-se with distinct preferences. We further show that a su bset of E(spl) proteins can heterodimerize with Da, another subset can heterodimerize with proneural proteins, and yet another with both, in dicating specialization within the E(spl) family, Hairy displays no in teractions with any of the HLH proteins tested, It does interact with the non-HLH protein Groucho, which itself interacts with all E(spl) ba sic HLH proteins, but with none of the proneural proteins or Da. We in vestigated the structural requirements for some of these interactions by site-specific and deletion mutagenesis.