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Journal of Virology, January 2000, p. 474-482, Vol. 74, No. 1
Laboratoire de Génétique des
Virus, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette Cedex, France
Received 2 June 1999/Accepted 20 September 1999
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 recognized a protein of
the expected size with late expression kinetics. This 57-kDa product
was also present in purified virions and was found to be associated
with all types of capsids. Synthesis of a protein migrating at the same
size point was directed from the eukaryotic expression plasmid
pCG-UL25. To determine the subcellular localization of UL25,
immunofluorescence studies with anti-UL25 antisera were performed on
Nonidet P-40-extracted COS-7 cells 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 distributed more
uniformly in the nucleus and colocalizes also with microtubules. To
study the fate of UL25 at very early stages of infection,
immunofluorescence experiments were performed on invading PrV particles
in the presence or absence of drugs that specifically depolymerize
components of the cytoskeleton. 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.
0022-538X/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The UL25 Protein of Pseudorabies Virus Associates
with Capsids and Localizes to the Nucleus and to Microtubules
*
Corresponding author. Mailing address: Laboratoire de
Virologie, Hôpital Saint-Vincent-de-Paul, 82 Ave.
Denfert-Rochereau, 75674 Paris Cedex 14, France. Phone:
33-1-40-48-82-41. Fax: 33-1-40-48-83-51. E-mail:
karin.kaelin{at}wanadoo.fr.
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