The UL13 virion protein of herpes simplex virus type 1 is phosphorylated by a novel virus-induced protein kinase.

Herpes simplex virus type 1 (HSV-1) induces a protein kinase (PK) activity in infected cell nuclei. In vitro, the enzyme is able to phosphorylate exogenous casein (albeit inefficiently) but not protamine, can use ATP or GTP as a phosphate donor, is stimulated by high salt concentrations and is insensitive to inhibition by heparin. On the basis of these properties, the PK appears to be distinct from previously described cellular enzymes and from the cytoplasmic PK encoded by the viral US3 gene. A major substrate of the enzyme in vitro is a virus-induced protein with an Mr of 57000 (Vmw57). The gene encoding Vmw57 was mapped using recombinants between HSV-1 and HSV-2 to a region of the virus genome containing genes UL9 to UL15. Use of a monospecific rabbit antiserum showed that Vmw57 is a virion structural protein encoded by gene UL13. These results, in conjunction with previous reports that the UL13 protein contains PK sequence motifs, support the notions that the nuclear PK and Vmw57 are identical, and that the observed reactivity is due to autophosphorylation.