Identification and characterization of proteins that interact with Drosophila melanogaster protein kinase CK2

D. melanogaster CK2 (DmCK2) is a highly conserved protein kinase that is co mposed of catalytic, alpha, and regulatory, beta, subunits associated as an alpha (2)beta (2) heterotetramer. In order to analyze the functions of CK2 in this metazoan model, we have used the two hybrid approach to identify i nteracting proteins. One of these cDNAs, DmA24, encodes a novel polypeptide with no homologs in GenBank, and is notable in that it contains a bipartit e nuclear localization signal and two sites for phosphorylation by CK2. In situ hybridization to polytene chromosomes indicates that the DmA24 gene is located at the 61D interval of chromosome II a region that also harbors 3 additional genes with similar structure. DmA24p interacts with DmCK2 alpha, but not with DmCK2 beta, demonstrating that this interaction is specific f or the catalytic subunit of CK2. In addition, the protein is phosphorylated by the holoenzyme purified from Drosophila embryos. These studies identify DmA24p as a potentially new physiological partner of DmCK2. In addition, w e also report the results of a large-scale screen that has identified a new set of DmCK2-interacting proteins. Most notable among these are Surf6, a n ucleolar protein involved in RNA processing, and Spalt, a homeotic protein.