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Journal of Virology, May 1999, p. 3866-3876, Vol. 73, No. 5
Department of Molecular Genetics and
Biochemistry, University of Pittsburgh, School of Medicine,
Pittsburgh, Pennsylvania 15261
Received 5 October 1998/Accepted 5 January 1999
Herpes simplex virus type 1 (HSV-1) establishes latency in sensory
neurons, a state in which the viral lytic genes are silenced and only
the latency locus is transcriptionally active, producing the 2.0- and
1.5-kb latency-associated transcripts (LATs). Previous experimental
evidence indicates that the LATs are stable introns, and it has been
reported that LAT formation is abolished by debilitating substitution
mutations in the predicted splice sites during lytic infection but not
latency (J. L. Arthur et al., J. Gen. Virol. 79:107-116,
1998). We have independently studied a set of deletion mutations to
explore the roles of the proposed splice sites during lytic and latent
infection. HSV-1 mutant viruses missing the invariant intron-terminal
5'-G(T/C) or 3'-AG dinucleotides were analyzed for LAT formation during
lytic infection in vitro, when only the 2-kb LAT is produced, and
during latency in mouse trigeminal ganglia, where both LATs are
expressed. Northern blot analysis of total RNAs from different
productively infected cell lines showed that the lytic (2-kb) LAT was
not expressed by the various splice site deletion mutants. In vivo
studies using a mouse eye model of latency similarly showed that the
latent (2- and 1.5-kb) LATs were not expressed by the mutants. PCR
analysis with primers flanking the LAT sequence revealed the expected
splice junction for LAT excision in RNA from sensory neurons latently
infected with wild-type but not mutant virus. Using a virus mutant
deleted in the splicing signals flanking the 556-bp region of LAT whose
absence distinguishes the 1.5- and 2-kb LATs, we observed selective
elimination of 1.5-kb LAT expression in latency, supporting previous
suggestions that the internal region is removed by splicing. Taken
together, these results demonstrate that the 2-kb LAT is formed during
both lytic and latent infection by splicing at the predicted splice
sites and that an additional splicing event is involved in the
latency-restricted production of the 1.5-kb LAT. We have also mapped
the 3' end of the lytic 2-kb LAT and discuss our results in the context
of previous models addressing the unusual stability of the LATs.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Genetic Studies Exposing the Splicing Events Involved in Herpes
Simplex Virus Type 1 Latency-Associated Transcript Production
during Lytic and Latent Infection
*
Corresponding author. Mailing address: Department of
Molecular Genetics and Biochemistry, University of Pittsburgh School of
Medicine, E1240 Biomedical Science Tower, Pittsburgh, PA 15261. Phone:
(412) 648-8106. Fax: (412) 624-8997. E-mail:
joe{at}hoffman.mgen.pitt.edu.
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