ABSTRACT
The translation elongation factor 1δ (EF-1δ) consists of two forms, a hypophosphorylated form (apparent M
r, 38,000) and a hyperphosphorylated form (apparentM
r, 40,000). Earlier Y. Kawaguchi, R. Bruni, and B. Roizman (J. Virol. 71:1019–1024, 1997) reported that whereas mock-infected cells accumulate the hypophosphorylated form, the hyperphosphorylated form of EF-1δ accumulates in cells infected with herpes simplex virus 1. We now report that the accumulation of the hyperphosphorylated EF-1δ is due to phosphorylation by UL13 protein kinase based on the following observations. (i) The relative amounts of hypo- and hyperphosphorylated EF-1δ in Vero cells infected with mutant virus lacking the UL13 gene could not be differentiated from those of mock-infected cells. In contrast, the hyperphosphorylated EF-1δ was the predominant form in Vero cells infected with wild-type viruses, a recombinant virus in which the deleted UL13 sequences were restored, or with a virus lacking the US3 gene, which also encodes a protein kinase. (ii) The absence of the hyperphosphorylated EF-1δ in cells infected with the UL13 deletion mutant was not due to failure of posttranslational modification of infected-cell protein 22 (ICP22)/US1.5 or of interaction with ICP0, inasmuch as preferential accumulation of hyperphosphorylated EF-1δ was observed in cells infected with viruses from which the genes encoding ICP22/US1.5 or ICP0 had been deleted. (iii) Both forms of EF-1δ were labeled by 32Pi in vivo, but the prevalence of the hyperphosphorylated EF-1δ was dependent on the presence of the UL13 protein. (iv) EF-1δ immunoprecipitated from uninfected Vero cells was phosphorylated by UL13 precipitated by the anti-UL13 antibody from lysates of wild-type virus-infected cells, but not by complexes formed by the interaction of the UL13 antibody with lysates of cells infected with a mutant lacking the UL13 gene. This is the first evidence that a viral protein kinase targets a cellular protein. Together with evidence that ICP0 also interacts with EF-1δ reported in the paper cited above, these data indicate that herpes simplex virus 1 has evolved a complex strategy for optimization of infected-cell protein synthesis.
Association of a M(r) 90,000 phosphoprotein with protein kinase PKR in cells exhibiting enhanced phosphorylation of translation initiation factor eIF-2 alpha and premature shutoff of protein synthesis after infection with gamma 134.5- mutants of herpes simplex virus 1.
