UL13 protein kinase of herpes simplex virus 1 complexes with glycoprotein E and mediates the phosphorylation of the viral Fc receptor:: Glycoproteins E and I

Herpes simplex virus 1 encodes a Fc receptor consisting of glycoproteins E(gE) and I (gl) and two protein kinases specified by U(L)13 and U(S)3, respectively. We report the following: (i) Antibody to U(L)13 formed immune complexes containing gE and gI in addition to U(L)13 protein. Immune complexes formed by monoclonal antibody to gE, but not those formed by monoclonal antibody to gI, also contained the U(L)13 protein. This association may reflect direct interaction between gE and U(L)13 inasmuch as IgG in preimmune rabbit serum and an antiserum made against another viral protein which does not react with the U(L)13 protein directly also bound gE and U(L)13. (ii) In cells infected with the wild-type virus, gE formed two sharp bands and a diffuse, slower migrating band. The slower sharp band was undetectable, and the diffuse slower migrating forms of gE were diminished in lysates of cells infected with a mutant virus lacking the U(L)13 gene (Delta U(L)13). (iii) Both gE and gI were labeled with (32)Pi in cells infected with wild-type or the Delta U(L)13 virus, but the labeling was significantly stronger in cells infected with the wild-type virus than in those infected with the Delta U(L)13 virus. (iv) In an in vitro protein kinase assay, U(L)13 immunoprecipitated from cells infected with wild-type virus labeled gE in the presence of [gamma-P-32]ATP. This activity was absent in precipitates from cells infected with Delta U(L)13 virus. The labeled gE comigrated with the slower, sharp band of gE. (v) gI present in the U(L)13 immune complex was also phosphorylated in the in vitro kinase assay. (vi) The cytoplasmic domain of gE contains recognition sequences for phosphorylation by casein kinase II (CKII). Exogenous CKII phosphorylated gE in immune complexes from lysates of cells infected with the Delta U(L)13 mutant or in immune complexes from lysates of cells infected with wild-type virus that had been heated to inactivate all endogenous kinase activity including that of U(L)13. In both instances, CKII phosphorylated gE in both the slow and fast migrating sharp bands. We conclude that U(L)13 physically associates with gE and mediates the phosphorylation of gE and gI. U(L)13 may also be a determinant in posttranslational processing of gE. (C) 1998 Academic Press.