The pseudorabies virus UL51 gene product is a 30-kilodalton virion component

Positional homologs to the UL51 open reading frame of herpes simplex virus type 1 have been identified throughout the herpesvirus family. However, no respective protein has so far been described for any of the herpesviruses. With rabbit antisera directed against oligopeptides predicted to comprise antigenic regions of the deduced pseudorabies virus (PrV) UL51 protein, a polypeptide with a size of 30 kDa was identified in PrV-infected cell lysates and in purified virions. This molecular mass correlates reasonably well with the predicted mass of 25 kDa of the 236-amino-acid deduced UL51 protein. Antisera raised against peptides derived from different predicted antigenic regions all detected the 30-kDa protein in Western blot (immunoblot) analyses. Specificity was ascertained by peptide competition. Subcellular fractionation showed the presence of the UL51 protein mainly in the nucleus of infected cells. After separation of purified virion preparations into envelope and capsid, the PrV UL51 protein was detected in the capsid fraction. In summary, we identified the first herpesvirus ULSI protein and demonstrate that it represents a structural component of PrV virions.