Identification of small DNA fragments synthesized in herpes simplex virus-infected cells in the presence of acyclovir

The effect of acyclovir on DNA synthesized in cells infected with herpes simplex virus type 1 was examined. DNA that was synthesized in infected cells in the presence of acyclovir during a short pulse with [3H]thymidine remained near the top of an alkaline sucrose gradient after centrifugation. The sedimentation characteristics of labeled DNA were not changed after chasing in isotope-free medium. The slowly sedimenting DNA was identified as viral in origin by hybridization to purified herpes simplex virus nucleocapsid DNA. When cells were infected with acyclovir-resistant virus containing mutations in the polymerase gene, the viral DNA synthesized in the presence of acyclovir was chased into high-molecular-weight DNA. These findings are consistent with chain termination of herpes simplex virus DNA in virus-infected cells.