The protein kinase encoded in the short unique region of pseudorabies virus: description of the gene and identification of its product in virions and in infected cells.

We have cloned and determined the nucleotide sequence of a gene, pk, that lies immediately upstream from the gene encoding glycoprotein X in the short unique region of the alphaherpesvirus, pseudorabies virus (PRV). The gene has the potential to encode a protein of 334 amino acids, and is related to gene US3 of herpes simplex virus type 1 (HSV-1), which has been shown to encode a protein kinase. The predicted amino acid sequence encoded by the PRV pk gene is homologous to the corresponding sequence encoded by the HSV-1 US3 gene in the C-terminal catalytic domain, but diverges markedly in the N-terminal domain. As with HSV-1, the mRNA for the pk gene appears to be 3' coterminal with that for the glycoprotein downstream. An antiserum was raised against a protein generated from the fusion of part of the PRV pk catalytic domain with Escherichia coli beta-galactosidase. This specifically reacted with a previously described physically homogeneous protein kinase, PRV-PK, isolated from hamster fibroblasts lytically infected with PRV. Although the majority of the PRV-PK is found in the cytoplasm, some was also detected in purified PRV virions by using the same antibody; a similar distribution was found for the HSV-1 protein kinase, using an antiserum raised against the corresponding HSV-1 fusion protein. When presented with heatinactivated virions, purified PRV-PK (in common with certain cellular protein kinases also present in the virion) was able to phosphorylate in vitro the major virion phosphoprotein phosphorylated in vivo.