DNA synthesis in chromatin preparations from human fibroblasts infected by cytomegalovirus.

Chromatin prepared from (14C)-thymidine pulse labelled cytomegalovirus-infected human fibroblasts 72 hours postinfection exhibited under appropriate conditions endogenous activity of (3H)-thymidine triphosphate incorporation which was relatively salt-resistant and phosphonoacetic acid-sensitive. Isopycnic centrifugation of the doubly labelled DNA in CsCl revealed that cell-free incoporation occurred into viral as well as into host cell DNA. Density labelling experiments with bromodeoxyuridine triphosphate suggested the incoporation into viral DNA to be due to replicative DNA synthesis. Chromatin from infected cells contained, in addition to cellular, viral DNA polymerase activity.