A Casein‐Kinase‐2‐Related Protein Kinase is Tightly Associated with the Large T Antigen of Simian Virus 40

Abstract

The simian virus 40 (SV40) large T antigen is a multifunctional protein 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‐transformed cells and from baculovirus‐infected insect cells is tightly associated with a protein kinase that phosphorylates T antigen in vitro. In the presence of heparin or a peptide resembling a protein kinase CK2 recognition site, the phosphorylation of T antigen by the associated kinase is reduced whereas a p34cdc2‐kinase‐specific peptide has no influence. In addition, the T‐antigen‐associated protein kinase can use GTP and ATP as phosphate donors. These properties together with the observation that immunopurified T antigen can be phosphorylated by the addition of protein kinase CK2 suggest that at least one of the T‐antigen‐associated protein kinases is CK2 or a protein‐kinase‐CK2‐related enzyme. The association of recombinant CK2 with T antigen was strongly confirmed by in vitro binding studies. Experiments with temperature‐sensitive SV40‐transformed cells provide evidence for a close correlation between cell transformation and phosphorylation of T antigen by the associated protein kinase. Copyright © 1995, Wiley Blackwell. All rights reserved