(E)-5-(2-bromovinyl)uridine requires phosphorylation by the herpes simplex virus (type 1)-induced thymidine kinase to express its antiviral activity.

(E)-5-(2-Bromovinyl)uridine (BVUrd), the riboside counterpart of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdUrd), effected a dose-dependent inhibition of viral progeny formation and viral DNA synthesis in herpes simplex virus type 1 (HSV-1, strain KOS)-infected human (E6SM) diploid fibroblast cells. BVUrd was directly phosphorylated in HSV-1-infected cells, presumably by the virus-encoded thymidine kinase (TK), since (i) BVUrd was not phosphorylated by extracts of cells infected with a HSV-1 strain deficient in TK expression and (ii) the phosphorylation was inhibited by a polyclonal anti-HSV-1 antibody. Within the HSV-1-infected cells, BVUrd was incorporated into the viral DNA as BVdUMP (BVdUrd 5'-monophosphate). This incorporation may account for the antiviral action of BVUrd, and implies that, following its initial phosphorylation by the viral TK, BVUrd is converted to its 2'-deoxy counterpart, most likely at the 5'-diphosphate level (BVUDP----BVdUDP).