Eukaryotic elongation factor 1δ is hyperphosphorylated by the protein kinase encoded by the UL13 gene of herpes simplex virus 1

The translation elongation factor 1 delta (EF-1 delta) consists of two forms, a hypophosphorylated form (apparent M-r, 38,000) and a hyperphosphorylated form (apparent M-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-1 delta accumulates in cells infected with herpes simplex virus 1. We now report that the accumulation of the hyperphosphorylated EF-1 delta is due to phosphorylation by U(L)13 protein kinase based on the following observations. (i) The relative amounts of hypo-and hyperphosphorylated EF-1 delta in Vero cells infected with mutant virus lacking the U(L)13 gene could not be differentiated from those of mock-infected cells. In contrast, the hyperphosphorylated EF-1 delta was the predominant form in Vero cells infected with wild-type viruses, a recombinant virus in which the deleted U(L)13 sequences were restored, or with a virus lacking the U(L)3 gene, which also encodes a protein kinase. (ii) The absence of the hyperphosphorylated EF-1 delta in cells infected with the U(L)13 deletion mutant was not due to failure of posttranslational modification of infected-cell protein 22 (ICP22)/U(S)1.5 or of interaction with ICP0, inasmuch as preferential accumulation of hyperphosphorylated EF-1 delta was observed in cells infected with viruses from which the genes encoding ICP22/U(S)1.5 or ICP0 had been deleted. (i) Both forms of EF-1 delta were labeled by P-32(i) in vivo, but the prevalence of the hyperphosphorylated EF-1 delta was dependent on the presence of the U(L)13 protein. (iv) EP-1 delta immunoprecipitated from uninfected Vero cells was phosphorylated by U(L)13 precipitated by the anti-U(L)13 antibody from lysates of mild-type virus-infected cells, but not by complexes formed qv the interaction of the U(L)13 antibody with lysates of cells infected with a mutant lacking the U(L)13 gene. This is the first evidence that a viral protein kinase targets a cellular protein. Together with evidence that ICPO also interacts with EF-1 delta 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.