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J. Virol., Jan 1996, 282-291, Vol 70, No. 1
GC Perng, K Chokephaibulkit, RL Thompson, NM Sawtell, SM Slanina, H Ghiasi, AB Nesburn and SL Wechsler
The goal of this report was to determine if the region of the LAT gene that
is colinear with ICP34.5 (kb 6.2 to 7.1 of LAT) is involved in spontaneous
reactivation of herpes simplex virus type 1. We inserted one copy of the
ICP34.5 gene into the unique long region of a herpes simplex virus type 1
(strain McKrae) mutant lacking both copies of ICP34.5 (one in each viral
long repeat) and the corresponding 917- nucleotide colinear portion of LAT
(kb 6.2 to 7.1). Rabbits were ocularly infected with this mutant, and
spontaneous reactivation relative to that for the wild-type virus and the
original mutant was measured. As we previously reported, the original
ICP34.5-deleted virus (d34.5) was significantly impaired for spontaneous
reactivation and virulence (G. C. Perng, R. L. Thompson, N. M. Sawtell, W.
E. Taylor, S. M. Slanina, H. Ghiasi, R. Kaiwar, A. B. Nesburn, and S. L.
Wechsler, J. Virol. 69:3033-3041, 1995). In contrast, we report here that
restoration of one copy of ICP34.5 at a distant location completely
restored the wild-type level of in vivo spontaneous reactivation, despite
retention of the deletion in LAT (spontaneous reactivation rate = 0.3 to
1.4% for the ICP34.5 deletion mutant, 7.7 to 19.6% for the wild type, and 9
to 16.1% for virus with one copy of ICP34.5). Thus, the 917-nucleotide
region of LAT from kb 6.2 to 7.1 was not involved in the LAT function
required for wild-type spontaneous reactivation. We also found that
restoration of a single ICP34.5 gene in a novel location did not restore
wild-type virulence (rabbit death rate = 0% [0 of 15] for the original
ICP34.5 deletion mutant, 8% [2 of 24] for the single-copy IPC34.5 virus,
and 52% [14 of 27] for wild-type virus; P < 0.001 for one versus two
copies of ICP34.5). It is likely that either two gene doses of ICP34.5 or
its location in the long repeat is essential for full functionality of
ICP34.5's virulence function. Furthermore, the ability of the single-copy
ICP34.5 virus to reactivate at wild-type levels despite being significantly
less virulent than wild- type virus separates the spontaneous reactivation
phenotype from the virulence phenotype.
Copyright © 1996, American Society for Microbiology
The region of the herpes simplex virus type 1 LAT gene that is colinear with the ICP34.5 gene is not involved in spontaneous reactivation
Ophthalmology Research Laboratories, Cedars-Sinai Medical Center Research Institute, Los Angeles, California 90048, USA.
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