We report on a protein kinase function encoded by the unique N terminus of the herpes simplex virus type 1 (HSV-1) ribonucleotide reductase large subunit (R1). Rl expressed in Escherichia coli exhibited autophosphorylation activity in a reaction which depended on the presence of the unique N terminus. When the N terminus was separately expressed in E. coli and partially purified, a similar autophosphorylation reaction was observed. Importantly, transphosphorylation of histones and of proteins

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... HSV-1-infected cell extracts was also observed with purified Rl and with truncated Rl mutants in which most of the N terminus was deleted. Ion-exchange chromatography was used to separate the autophosphorylating activity of the N terminus from the transphosphorylating activity of an E. coli contaminant protein kinase. We propose a putative function for this activity of the HSV-1 Rl N terminus during the immediate-early phase of virus replication.