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J. Virol., 10 1995, 5959-5968, Vol 69, No. 10
S Schmolke, HF Kern, P Drescher, G Jahn and B Plachter
The phosphoprotein pp65 (ppUL83) of human cytomegalovirus (HCMV) is
abundantly synthesized during lytic infection in cultured fibroblasts. As a
major constituent of extracellular particles, it gains entry to infected
cells immediately after adsorption and subsequently translocates to the
cell nucleus. This efficient transport is mediated by unique nuclear
localization signals. To study the function of pp65, a viral deletion
mutant was constructed by replacing the pp65 gene with the bacterial
neomycin phosphotransferase gene, driven by the simian virus 40 early
promoter. The resulting virus, RVAd65, could be grown and selected on human
fibroblasts without complementation. The deletion of the pp65 gene in
RVAd65 was verified by using Southern blot and PCR analyses. The lack of
expression from the gene was investigated by immunoblotting with
pp65-specific monoclonal antibodies. Single-cycle growth analyses showed
that RVAd65 grew to levels of infectivity comparable to those of the
wild-type virus. Therefore, pp65 is nonessential for the growth of HCMV in
human fibroblasts. Electron microscopy revealed no differences in the
processes of virion morphogenesis, although the maturation appeared to be
delayed. However, the kinetics of expression of the immediate-early genes
UL122 and UL123, the early gene UL44, and the late gene UL32 were the same
in RVAd65-infected cells as in wild-type virus-infected cells in immunoblot
analyses. In vitro phosphorylation assays showed that some of the virion
proteins were labelled to a markedly reduced extent by virion-associated
kinases in RVAd65 compared with wild-type virus. We therefore conclude that
although deletion of the pp65 gene does not abolish replication of HCMV, a
recombinant virus lacking pp65 displays phenotypic alterations compared
with wild-type virus during growth in cultured fibroblasts.
Copyright © 1995, American Society for Microbiology
The dominant phosphoprotein pp65 (UL83) of human cytomegalovirus is dispensable for growth in cell culture
Institut fur Klinische und Molekulare Virologie, Universitat Erlangen- Nurnberg, Germany.
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