EUKARYOTIC ELONGATION-FACTOR-1-DELTA IS HYPERPHOSPHORYLATED BY THE PROTEIN-KINASE ENCODED BY THE U(L)13 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 hyperph osphorylated form (apparent M-r, 40,000). Earlier Y. Kawaguchi, R. Bru ni, and B. Roizman (J. Virol. 71:1019-1024, 1997) reported that wherea s mock-infected cells accumulate the hypophosphorylated form, the hype rphosphorylated form of EF-1 delta accumulates in cells infected with herpes simplex virus 1. We now report that the accumulation of the hyp erphosphorylated EF-1 delta is due to phosphorylation by U(L)13 protei n kinase based on the following observations. (i) The relative amounts of hypo-and hyperphosphorylated EF-1 delta in Vero cells infected wit h mutant virus lacking the U(L)13 gene could not be differentiated fro m those of mock-infected cells. In contrast, the hyperphosphorylated E F-1 delta was the predominant form in Vero cells infected with wild-ty pe 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 enco des 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 t o failure of posttranslational modification of infected-cell protein 2 2 (ICP22)/U(S)1.5 or of interaction with ICP0, inasmuch as preferentia l 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 delt a 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-ty pe virus-infected cells, but not by complexes formed qv the interactio n 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 prote in kinase targets a cellular protein. Together with evidence that ICPO also interacts with EF-1 delta reported in the paper cited above, the se data indicate that herpes simplex virus 1 has evolved a complex str ategy for optimization of infected-cell protein synthesis.