The HSV-1 UL45 18 kDa gene product is a true late protein and a component of the virion.

Previously we constructed a null mutation in the HSV-1 UL45 gene, showed that the UL45 gene was not required for growth in Vero cells, and confirmed that it coded for an 18 kDa protein (R.J. Visalli and C.R. Brandt, Virology 185:419-423, 1991). In this study, we have continued our characterization of the UL45 gene and the 18 kDa protein. Analysis of UL45 RNA revealed that the gene was expressed late and was inhibited in the presence of phosphonoacetic acid (paa), indicating it is a gamma 2 class gene. Using a specific polyclonal antiserum, we found that the 18 kDa UL45 gene product was also expressed late and was inhibited in the presence of paa. The 18 kDa protein was present in purified virions and was substantially enriched in the envelope-tegument fraction of virions disrupted with NP-40 detergent. The 18 kDa protein is thus a structural protein of the virus and appears to be associated with the viral envelope. A 20 kDa protein that cross-reacted with a polyclonal HSV-1 UL45 antiserum was also detected in cells infected with HSV-2 strain 333.