Identification of the UL4 protein of herpes simplex virus type 1

Herpes simplex virus type 1 gene UL4 is predicted to encode a 199-amino-aci d protein with a molecular mass of 21.5 kDa. We report here identification of this protein and its localization in the nuclei of infected cells. Antis era raised against oligopeptides corresponding to the C terminus of the pre dicted UL4 protein were used for identification of a 25 kDa protein as the product of the UL4 gene. This protein was not detected in cells infected wi th a UL4 defective mutant virus, but was synthesized by coupled in vitro tr anscription-translation of the UL4 gene. Synthesis of the 25 kDa protein wa s blocked by phosphonoacetic acid, an inhibitor of DNA synthesis, indicatin g that the UL4 gene is expressed with gamma kinetics. Subcellular fractiona tion showed the protein to be localized in the nucleus. It was not detected in virions or light particles.