Allosteric regulation of even-skipped repression activity by phosphorylation

The Drosophila homeodomain protein Even-skipped (Eve) is a well characteriz ed transcriptional repressor. Here, we show that Eve's ability to function in vitro is negatively regulated by phosphorylation. DNA-binding activity w as unaffected by phosphorylation, but phosphorylated Eve was unable to inte ract with the TATA-binding protein (TBP), a known target for repression. Un expectedly, phosphorylation of the Eve N terminus, which is dispensable for repression and TBP binding, was necessary and sufficient to inactivate Eve . LiCl, which specifically inhibits glycogen synthase kinase-3 (GSK-3), red uced Eve phosphorylation in nuclear extract and blocked inhibition of repre ssion. In addition, Eve was phosphorylated and inactivated by purified GSK- 3 beta plus casein kinase II. Our results suggest a novel mechanism of tran scriptional control involving phosphorylation-induced allosteric interferen ce with a repressive protein-protein interaction.