Characterization of the UL33 Gene Product of Herpes Simplex Virus 1

Abstract

The UL33 protein is one of six genes (including UL6, UL15, UL17, UL28, and UL32) required for cleavage of viral concatemeric DNA into unit-length genomes and packaging of the virus genomes into preformed capsids. The UL25 gene product is dispensable for cleavage of viral DNA but essential for packaging of DNA into capsids. A polyclonal antiserum was produced against an affinity-purified protein containing the full-length UL33 gene product of herpes simplex virus 1 fused to glutathione-S-transferase. A protein of approximate Mr 19,000 that reacted with the antiserum was detected in immunoblots of herpes simplex virus 1-infected cellular lysates. This protein was not detected in lysates of mock-infected cells or cells infected with a mutant virus containing a stop codon in UL33, indicating that the 19,000 Mr protein is the product of the UL33 open reading frame. The UL33 gene product was not detected in purified virions or capsids. Accumulation of the UL33 protein to detectable levels required viral DNA synthesis, indicating that the protein was regulated as a late gene. Indirect immunofluorescence analysis demonstrated that UL33 protein accumulated predominantly within replication compartments in the central domains of infected cell nuclei and within the cytoplasm. Localization of the UL33 gene product in replication compartments was maintained in cells infected with a variety of cleavage/packaging mutants.