A CASEIN-KINASE-2-RELATED PROTEIN-KINASE IS TIGHTLY ASSOCIATED WITH THE LARGE T-ANTIGEN OF SIMIAN-VIRUS-40

The simian virus 40 (SV40) large T antigen is a multifunctional protei n involved in SV40 cell transformation and lytic virus infection. Some of its activities are regulated by interaction with cellular proteins and/or by phosphorylation of T antigen by various protein kinases. In this study, we show that immunopurified T antigen from SV40-transform ed cells and from baculovirus-infected insect cells is tightly associa ted with a protein kinase that phosphorylates T antigen in vitro. In t he presence of heparin or a peptide resembling a protein kinase CK2 re cognition site, the phosphorylation of T antigen by the associated kin ase is reduced whereas a p34(cdc2)-kinase-specific peptide has no infl uence. In addition, the T-antigen-associated protein kinase can use GT P and ATP as phosphate donors. These properties together with the obse rvation that immunopurified T antigen can be phosphorylated by the add ition of protein kinase CK2 suggest that at least one of the T-antigen -associated protein kinases is CK2 or a protein-kinase-CK2-related enz yme. The association of recombinant CK2 with T antigen was strongly co nfirmed by in vitro binding studies. Experiments with temperature-sens itive SV40-transformed cells provide evidence for a close correlation between cell transformation and phosphorylation of T antigen by the as sociated protein kinase.