The Carboxyl-Terminal Domain of RNA Polymerase II Is Phosphorylated by a Complex Containing cdk9 and Infected-Cell Protein 22 of Herpes Simplex Virus 1

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Abstract
The infected-cell protein 22 (ICP22), a regulatory protein encoded by the α22 gene of herpes simplex virus 1, is required for the optimal expression of a set of late viral proteins that includes the products of the U S 11, U L 38, and U L 41 genes. ICP22 has two activities. Thus, ICP22 and the U L 13 protein kinase mediate the activation of cdc2 and degradation of its partners, cyclins A and B. cdc2 and its new partner, the DNA polymerase accessory factor (U L 42), bind topoisomerase IIα in an ICP22-dependent manner. In addition, ICP22 and U L 13 mediate an intermediate phosphorylation of the carboxyl terminus of RNA polymerase II (RNA POL II). Here we report another function of ICP22. Thus, ICP22 physically interacts with cdk9, a constitutively active cyclin-dependent kinase involved in transcriptional regulation. A protein complex containing ICP22 and cdk9 phosphorylates in vitro the carboxyl-terminal domain of RNA POL II in a viral U S 3 protein kinase-dependent fashion. Finally, the carboxyl-terminal domain of RNA POL II fused to glutathione S -transferase is phosphorylated in reaction mixtures containing complexes pulled down with ICP22 or cdk9 immune precipitated from lysates of wild-type parent virus or ΔU L 13 but not ΔU S 3 mutant-infected cells. The experiments described here place ICP22 and cdk9 in a complex with the carboxyl-terminal domain of RNA POL II. At the same time we confirm the requirement of ICP22 and the U L 13 protein kinase in the posttranslational modification of RNA POL II that alters its electrophoretic mobility, although U S 3 kinase appears to play a role in a cell-type-dependent fashion.