In vivo interactions of the Drosophila Hairy and Runt transcriptional repressors with target promoters

The Hairy and Runt pair-rule proteins regulate Drosophila segmentation by repressing transcription. To explore the ability of these proteins to function as promoter-bound regulators in vivo, we examined the effects of Hairy and Runt derivatives containing heterologous transcriptional activation domains (Hairy(Act) and Run(Act)). Using this approach, we find that Hairy and Runt efficiently target such activation domains to specific segmentation gene promoters, leading to rapid induction of transcription. Our results strongly suggest that Hairy normally acts as a promoter-bound repressor of fushi tarazu, runt and odd-skipped, and that Runt directly represses even-skipped. We also show that expressing Hairy(Act) in early blastoderm embryos causes ectopic Sex-lethal expression and mate-specific lethality, implying that the Hairy-related denominator element Deadpan represses Sex-lethal during sex determination by directly recognizing the early Sex-lethal promoter.