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J Virol, April 1998, p. 3307-3320, Vol. 72, No. 4
Department of Molecular Genetics and
Biochemistry, University of Pittsburgh School of Medicine,
Pittsburgh, Pennsylvania 15261
Received 21 November 1997/Accepted 7 January 1998
The immediate-early (IE) proteins of herpes simplex virus (HSV)
function on input genomes and affect many aspects of host cell
metabolism to ensure the efficient expression and regulation of the
remainder of the genome and, subsequently, the production of progeny
virions. Due to the many and varied effects of IE proteins on host cell
metabolism, their expression is not conducive to normal cell function
and viability. This presents a major impediment to the use of HSV as a
vector system. In this study, we describe a series of ICP4 mutants that
are defective in different subsets of the remaining IE genes. One
mutant, d109, does not express any of the IE proteins and
carries a green fluorescent protein (GFP) transgene under the control
of the human cytomegalovirus IE promoter (HCMVIEp). d109
was nontoxic to Vero and human embryonic lung (HEL) cells at all
multiplicities of infection tested and was capable of establishing
persistent infections in both of these cell types. Paradoxically, the
genetic manipulations that were required to eliminate toxicity and
allow the genome to persist in cells for long periods of time also
dramatically lowered the level of transgene expression. Efficient
expression of the HCMVIEp-GFP transgene in the absence of ICP4 was
dependent on the ICP0 protein. In d109-infected cells, the
level of transgene expression was very low in most cells but abundant
in a small subpopulation of cells. However, expression of the transgene
could be induced in cells containing quiescent d109 genomes
weeks after the initial infection, demonstrating the functionality of
the persisting genomes.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Persistence and Expression of the Herpes Simplex
Virus Genome in the Absence of Immediate-Early Proteins
*
Corresponding author. Mailing address: E1257 Biomedical
Science Tower, Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261. Phone: (412) 648-9947. Fax: (412) 624-1401. E-mail:
neal{at}hoffman.mgen.pitt.edu.
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