Human cytomegalovirus (HCMV), purified exclusively from the extracellular media, contained a DNA polymerase activity in addition to a protein kinase activity. The DNA polymerase expressed its maximum activity in the presence of 5 to 10 m-MgCl. The enzyme was able to use effectively activated calf thymus DNA, poly(dA).oligo(dT) and poly(dC).oligo(dG) as the template primers. The DNA polymerizing activity was eluted with 0.18 to 0.2 -KCl from a phosphocellulose column. It was relatively resistant to phosphonoacetic acid inhibition even at a high concentration of 100 µg/ml with activated calf thymus DNA as the template primer, but the DNA polymerase activity was totally suppressed at this concentration when poly(dA).oligo(dT) was used as the template primer. The enzyme activity was inhibited by ammonium sulphate at 0.01 to 0.3 with either activated calf thymus DNA or poly(dA).oligo(dT) as the template primer. The protein kinase has maximum activity in the presence of 10 to 20 m-MgCl, and preferred virion proteins as phospho-acceptor to protamine sulphate. Histone, caesin and bovine serum albumin (BSA) were found to be poor substrates. The phosphorylated protein pattern of the [P]orthophosphate-labelled virions was not identical to that of the phosphorylated Nonidet P40-dissociated virions, although seven phosphorylated polypeptides did co-migrate in SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Procedures known to solubilize virions showed that the DNA polymerase and protein kinase were internal components of the virion.


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