Characterization of human cytomegalovirus-induced DNA polymerase and the associated 3'-to-5', exonuclease.

A DNA polymerase activity induced by human cytomegalovirus (HCMV) was separated from host cell DNA polymerase and purified by phosphocellulose and DNA-cellulose column chromatography. The DNA polymerase activity was strongly inhibited by phosphonoacetic acid, aphidicolin, araATP, and N-ethylmaleimide, but it was resistant to 2',3'-dideoxyTTP. The sensitivity of HCMV-induced DNA polymerase to these reagents resembles that of host cell DNA polymerase alpha. However, HCMV-induced DNA polymerase activity was stimulated several fold by 100 mM ammonium sulfate, by which DNA polymerase alpha activity was strongly inhibited. Furthermore, it was found that a 3'-to-5' exonuclease activity was tightly associated with the HCMV-induced DNA polymerase. The exonuclease was also stimulated by ammonium sulfate, was inhibited by phosphoacetic acid, and it preferred single-stranded DNA as a substrate. The results suggest that the 3'-to-5' exonuclease may play a role in proofreading in the polymerization process as an integral part of the HCMV-induced DNA polymerase.