K. Kaelin et al., The UL25 protein of pseudorabies virus associates with capsids and localizes to the nucleus and to microtubules, J VIROLOGY, 74(1), 2000, pp. 474-482
The UL25 gene of pseudorabies virus (PrV) can encode a protein of about 57
kDa which is well conserved among herpesviruses, The UL25 protein of herpes
simplex virus type 1 is a capsid constituent involved in virus penetration
and capsid maturation. To identify and characterize the UL25 gene product
of PrV, polyclonal mouse anti-UL25 antibodies were raised to a bacterially
expressed fusion protein. In immunoblotting and immunoprecipitation assays
of PrV-infected cell lysates, these anti-UL25 antisera specifically recogni
zed a protein of the expected size with late expression kinetics. This 57-k
Da product was also present in purified virions and was found to be associa
ted with all types of capsids. Synthesis of a protein migrating at the same
size point was directed from the eukaryotic expression plasmid pCG-UL25. T
o determine the subcellular localization of UL25, immunofluorescence studie
s with anti-UL25 antisera were performed on Nonidet P-40-extracted COS-7 ce
lls infected with PrV or transfected with pCG-UL25. In PRV-infected cells,
newly synthesized UL25 is directed mainly to distinct nuclear compartments,
whereas UL25 expressed in the absence of other viral proteins is distribut
ed more uniformly in the nucleus and colocalizes also with microtubules. To
study the fate of UL25 at very early stages of infection, immunofluorescen
ce experiments were performed on invading PrV particles in the presence or
absence of drugs that specifically depolymerize components of the cytoskele
ton. We found that the incoming nucleocapsids colocalize with microtubules
during their transport to the nucleus and that UL25 remains associated with
nucleocapsids during this transport.