J Virol, May 1998, p. 3779-3788, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Veterinary Education Center, Department of Microbiology and Immunology, Cornell University, Ithaca, New York 14853,1 and MRC Virology Unit, Glasgow G11 5JR, United Kingdom2
Received 3 November 1997/Accepted 15 January 1998
Previous studies have suggested that the UL17 gene of
herpes simplex virus type 1 (HSV-1) is essential for virus replication. In this study, viral mutants incorporating either a lacZ
expression cassette in place of 1,490 bp of the 2,109-bp
UL17 open reading frame [HSV-1(
UL17)] or a
DNA oligomer containing an in-frame stop codon inserted 778 bp from the
5' end of the UL17 open reading frame
[HSV-1(UL17-stop)] were plaque purified on engineered
cell lines containing the UL17 gene. A virus derived from
HSV-1(UL17-stop) but containing a restored UL17
gene was also constructed and was designated
HSV-1(UL17-restored). The latter virus formed plaques and
cleaved genomic viral DNA in a manner indistinguishable from wild-type
virus. Neither HSV-1(
UL17) nor
HSV-1(UL17-stop) formed plaques or produced infectious
progeny when propagated on noncomplementing Vero cells. Furthermore,
genomic end-specific restriction fragments were not detected in DNA
purified from noncomplementing cells infected with
HSV-1(
UL17) or HSV-1(UL17-stop), whereas
end-specific fragments were readily detected when the viruses were
propagated on complementing cells. Electron micrographs of thin
sections of cells infected with HSV-1(
UL17) or
HSV-1(UL17-stop) illustrated that empty capsids accumulated
in the nuclei of Vero cells, whereas DNA-containing capsids accumulated
in the nuclei of complementing cells and enveloped virions were found
in the cytoplasm and extracellular space. Additionally, protein
profiles of capsids purified from cells infected with
HSV-1(
UL17) compared to wild-type virus show no
detectable differences. These data indicate that the UL17
gene is essential for virus replication and is required for cleavage and packaging of viral DNA. To characterize the UL17 gene
product, an anti-UL17 rabbit polyclonal antiserum was
produced. The antiserum reacted strongly with a major protein of
apparent Mr 77,000 and weakly with a protein of
apparent Mr 72,000 in wild-type infected cell
lysates and in virions. Bands of similar sizes were also detected in
electrophoretically separated tegument fractions of virions and light
particles and yielded tryptic peptides of masses characteristic of the
predicted UL17 protein. We therefore conclude that the
UL17 gene products are associated with the virion tegument and note that they are the first tegument-associated proteins shown to
be required for cleavage and packaging of viral DNA.
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