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J Virol, March 1998, p. 2463-2473, Vol. 72, No. 3
Department of Microbiology, University of
Connecticut Health Center, Farmington, Connecticut 06030-3205
Received 25 September 1997/Accepted 10 December 1997
Six genes, including UL32, have been implicated in the cleavage and
packaging of herpesvirus DNA into preassembled capsids. We have
isolated a UL32 insertion mutant which is capable of near-wild-type levels of viral DNA synthesis; however, the mutant virus is unable to
cleave and package viral DNA, consistent with the phenotype of a
previously isolated temperature-sensitive herpes simplex virus type 1 mutant, tsN20 (P. A. Schaffer, G. M. Aron, N. Biswal, and M. Benyesh-Melnick, Virology 52:57-71, 1973). A polyclonal antibody which recognizes UL32 was previously used by Chang et al.
(Y. E. Chang, A. P. Poon, and B. Roizman, J. Virol.
70:3938-3946, 1996) to demonstrate that UL32 accumulates predominantly
in the cytoplasm of infected cells. In this report, a functional
epitope-tagged version of UL32 showed that while UL32 is predominantly
cytoplasmic, some nuclear staining which colocalizes with the major DNA
binding protein (ICP8, UL29) in replication compartments can be
detected. We have also used a monoclonal antibody (5C) specific for the hexon form of major capsid protein VP5 to study the distribution of
capsids during infection. In cells infected with wild-type KOS (6 and
8 h postinfection), 5C staining patterns indicate that capsids are
present in nuclei within replication compartments. These results
suggest that cleavage and packaging occur in replication compartments
at least at 6 and 8 h postinfection. Cells infected with the UL32
mutant exhibit a hexon staining pattern which is more diffusely
distributed throughout the nucleus and which is not restricted to
replication compartments. We propose that UL32 may play a role in
"bringing" preassembled capsids to the sites of DNA packaging and
that the failure to localize to replication compartments may explain
the cleavage/packaging defect exhibited by this mutant. These results
suggest that the UL32 protein is required at a step distinct from those
at which other cleavage and packaging proteins are required and may be
involved in the correct localization of capsids within infected cells.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
The Herpes Simplex Virus Type 1 Cleavage/Packaging Protein,
UL32, Is Involved in Efficient Localization of Capsids to
Replication Compartments
*
Corresponding author. Mailing address: Department of
Microbiology, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06030-3205. Phone: (860) 679-2310. Fax: (860) 679-1239. E-mail: Weller{at}nso2.uchc.edu.
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