Hairy is a repressor that regulates bristle patterning, and its loss elicits ectopic bristles (neural hyperplasia). However, it has remained unknown whether Hairy is regulated by phosphorylation. We describe here the interaction Of Protein kinase CK2 and Hairy. Hairy is robustly phosphorylated by the CK2-holo-enzyme (CK2-HoloE) purified from Drosophila embryos, but weakly by the catalytic CK2 alpha-subunit alone, suggesting that this interaction requires the regulatory CK2 beta-subunit. Consistent with this, Hairy preferentially forms a direct complex with CK2-HoloE. Importantly, we demonstrate genetic interactions between CK2 and hairy (h). Thus, flies trans-heterozygous for alleles of CK2 alpha and h display neural hyperplasia akin to homozygous hypomorphic h alleles. In addition, we show that similar phenotypes are elicited in wild-type flies upon expression of RNAi constructs against CK2 alpha/beta, and that these defects are sensitive to h gene dosage. Together, these studies suggest that CK2 contributes to repression by Hairy. (c) 2008 Elsevier Inc. All rights reserved