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Journal of Virology, March 1999, p. 2321-2332, Vol. 73, No. 3
Center for Immunology and Departments of
Pathology and Molecular Microbiology, Washington University School
of Medicine, St. Louis, Missouri 63110
Received 28 September 1998/Accepted 3 December 1998
The program(s) of gene expression operating during murine
gammaherpesvirus 68 (
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Three Distinct Regions of the Murine Gammaherpesvirus 68 Genome
Are Transcriptionally Active in Latently Infected Mice
HV68) latency is undefined, as is the
relationship between
HV68 latency and latency of primate
gammaherpesviruses. We used a nested reverse transcriptase PCR strategy
(sensitive to approximately one copy of
HV68 genome for each genomic
region tested) to screen for the presence of viral transcripts in
latently infected mice. Based on the positions of known
latency-associated genes in other gammaherpesviruses, we screened for
the presence of transcripts corresponding to 11 open reading frames
(ORFs) in the
HV68 genome in RNA from spleens and peritoneal cells
of latently infected B-cell-deficient (MuMT) mice which have been shown
contain high levels of reactivable latent
HV68 (K. E. Weck, M. L. Barkon, L. I. Yoo, S. H. Speck, and H. W. Virgin, J. Virol. 70:6775-6780, 1996). To control for the
possible presence of viral lytic activity, we determined that RNA from
latently infected peritoneal and spleen cells contained few or no
detectable transcripts corresponding to seven ORFs known to encode
viral gene products associated with lytic replication. However, we did
detect low-level expression of transcripts arising from the region of
gene 50 (encoding the putative homolog of the Epstein-Barr virus BRLF1
transactivator) in peritoneal but not spleen cells. Latently infected
peritoneal cells consistently scored for expression of RNA derived from
4 of the 11 candidate latency-associated ORFs examined, including the
regions of ORF M2, ORF M11 (encoding v-bcl-2), gene 73 (a homolog of
the Kaposi's sarcoma-associated herpesvirus [human herpesvirus 8]
gene encoding latency-associated nuclear antigen), and gene 74 (encoding a G-protein coupled receptor homolog, v-GCR). Latently
infected spleen cells consistently scored positive for RNA derived from
3 of the 11 candidate latency-associated ORFs examined, including ORF
M2, ORF M3, and ORF M9. To further characterize transcription of these
candidate latency-associated ORFs, we examined their transcription in
lytically infected fibroblasts by Northern analysis. We detected
abundant transcription from regions of the genome containing ORF M3 and
ORF M9, as well as the known lytic-cycle genes. However,
transcription of ORF M2, ORF M11, gene 73, and gene 74 was barely
detectable in lytically infected fibroblasts, consistent with a role of
these viral genes during latent infection. We conclude that (i) we have
identified several candidate latency genes of murine
HV68, (ii)
expression of genes during latency may be different in different
organs, consistent with multiple latency programs and/or multiple
cellular sites of latency, and (iii) regions of the viral genome
(v-bcl-2 gene, v-GCR gene, and gene 73) are transcribed during latency
with both
HV68 and primate gammaherpesviruses. The implications of
these findings for replacing previous operational definitions of
HV68 latency with a molecular definition are discussed.
*
Corresponding author. Mailing address: Center for
Immunology and Departments of Pathology and Molecular Microbiology,
Washington University School of Medicine, Box 8118, 660 S. Euclid Ave.,
St. Louis, MO 63110. Phone: (314) 362-0367 (S.H.S.) and (314) 362-9223 (H.W.V.). Fax: (314) 362-4096. E-mail:
virgin{at}immunology.wustl.edu (H.W.V.) and
speck{at}pathology.wustl.edu (S.H.S.).
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