The pseudorabies virus DNA polymerase processivity factor UL42 exists as a monomer in vitro and in vivo

The processivity factors (PFs) of herpesviruses confer processivity to the DNA polymerase. Understanding whether the herpesvirus PFs function as monomers or multimers is important for clarifying the mechanism by which they provide the DNA polymerase with processivity. Herpes simplex virus type 1 UL42 is a monomer, whereas human cytomegalovirus UL44, Epstein-Barr virus BMRF1, and Kaposi's sarcoma-associated herpesvirus PF-8 exist as dimers. However, the oligomeric status of the pseudorabies virus (PRV) DNA polymerase PF UL42 has not been determined. Using fluorescence confocal microscopy and chemical crosslinking, we confirmed that UL42 is a monomer when expressed in vitro. Crosslinking of nuclear extracts from PRV-infected or uninfected PK-15 cells verified that UL42 exists as a monomer in vivo. Our demonstration that UL42 exists as a monomer in vitro and in vivo contributes to the further investigation of the mechanism used by UL42 to achieve processivity.