The envelope of human cytomegalovirus has been reported to contain between three and eight glycoproteins. Major constituents of the envelope include two abundant glycoproteins with estimated molecular weights of 55,000 (gp55) and 116,000 (gpll6). These two glycoproteins have been shown to exist as a disulfide-linked complex (gp55-116) within the envelope of mature virions. Utilizing a panel of monoclonal antibodies reactive with the gp55-116 complex, we characterized the synthesis and processing of these two virion proteins. Infected cells were shown to contain two glycosylated proteins of 160,000 and 150,000 daltons as well as the mature gp55 and gpll6. Pulse-chase analysis indicated that gpl50 was a precursor protein of gp160. The mature gp55 and gpll6 were generated, in turn, by cleavage of gp160. Antigenic and structural analysis revealed that gp55 and gpll6 shared little structural homology and no detectable antigenic cross-reactivity. The results of this study are discussed in relation to the synthesis of envelope proteins of other herpesviruses.

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Protein kinase activity was detected in immunoprecipitates of human cytomegalovirus virions and infected cells by using a monoclonal antibody directed against an abundant 68,000-dalton virion structural protein. Purification of this protein by electrophoresis confirmed that the kinase activity was associated with this protein. The kinase activity was dependent on divalent cations (Mg2+, Mn2+) and cyclic nucleotide independent and exhibited optimal activity at pH 7 to 8. The kinase phosphorylated threonine and serine but not tyrosine.

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