The human cytomegalovirus UL97 protein is phosphorylated and a component of virions

The expression of the human cytomegalovirus (HCMV) UL97 open reading frame in infected or transfected cells in the presence of the antiherpes compound ganciclovir (GCV) results in the intracellular phosphorylation of GCV. There are conventional kinase domains within the UL97-encoded protein (pUL97). However, the role of pUL97 in the HCMV replication cycle, and the mechanism by which it causes phosphorylation of GCV, are currently unknown. Herein, the biosynthesis and biogenesis of pUL97 was studied in HCMV-infected cells. pUL97 is expressed with early-late kinetics and is posttranslationally modified by phosphorylation. This phosphorylation occurs within 1 hr after synthesis, affects the electrophoretic mobility of pUL97, and is independent of the presence of other HCMV proteins. pUL97 was localized to the nucleus of infected cells and found in the HCMV virions. Thus, pUL97 is a virion phosphoprotein, and a likely tegument component.