Differential effects of 5-methylmercapto-2'-deoxyuridine on the replication of herpes simplex virus type 1 in two cell systems.

5-Methylmercapto-2'-deoxyuridine (MeMUdR), a structural analogue of thymidine (TdR), inhibits herpes simplex virus type 1 production in mouse L (Lb) cells at concentrations that are not inhibitory to viral growth in monkey kidney (CV-1) cells. It is moderately toxic to Lb cells but not to CV-1 cells at a concentration that causes 95% inhibition of viral replication in Lb cells. MeMUdR is incorporated into cellular and viral deoxyribonucleic acid (DNA) in both systems, but to a significantly higher level (compared with thymidine) in Lb cells. These results indicate that MeMUdR is a substrate for enzymes leading to DNA synthesis and suggest that the biological function of herpes simplex virus type 1 DNA is impaired only when the incorporation of MeMUdR into the DNA reaches a relatively high level.