DROSOPHILA CTBP - A HAIRY-INTERACTING PROTEIN REQUIRED FOR EMBRYONIC SEGMENTATION AND HAIRY-MEDIATED TRANSCRIPTIONAL REPRESSION

hairy is a Drosophila pair-rule segmentation gene that functions genet ically as a repressor. To isolate protein components of Hairy-mediated repression, we used a yeast interaction screen and identified a Hairy -interacting protein, the Drosophila homolog of the human C-terminal-b inding protein (CtBP). Human CtBP is a cellular phosphoprotein that in teracts with the C-terminus of the adenovirus E1a oncoprotein and func tions as a tumor suppressor. dCtBP also interacts with E1a in a direct ed yeast two-hybrid assay. We show that dCtBP interacts specifically a nd directly with a small, previously uncharacterized C-terminal region of Hairy. dCtBP activity appears to be specific to Hairy of the Hairy /Enhancer of split [E(spl)]/Dpn basic helix-loop-helix protein class. We identified a P-element insertion within the dCtBP transcription uni t that fails to complement alleles of a known locus, l(3)87De. We demo nstrate that dCtBP is essential for proper embryonic segmentation by a nalyzing embryos lacking maternal dCtBP activity. While Hairy is proba bly not the only segmentation gene interacting with dCtBP, we show dos e-sensitive genetic interactions between dCtBP and hairy mutations.