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

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 s pontaneous reactivation of herpes simplex virus type 1. We inserted on e copy of the ICP34.5 gene into the unique long region of a herpes sim plex 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 infect ed with this mutant, and spontaneous reactivation relative to that for the wild-type virus and the original mutant was measured, As we previ ously reported, the original ICP34.5-deleted virus (d34.5) was signifi cantly impaired for spontaneous reactivation and virulence (G. C. Pern g, R. L. Thompson, N. M. Sawtell, W. E. Taylor, S. M. Slanina, H. Ghia si, R. Kaiwar, A. B. Nesburn, and S. L. Wechsler, J. Virol, 69:3033-30 41, 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 deletio n 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 vi rus,vith 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 w ild-type spontaneous reactivation, We also found that restoration of a single ICP34.5 gene in a novel location did not restore wild-type vir ulence (rabbit death rate = 0% [0 of 15] for the original ICP34.5 dele tion 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 lo cation in the long repeat is essential for full functionality of ICP34 .5's virulence function, Furthermore, the ability of the single-copy I CP34.5 virus to reactivate at wild-type levels despite being significa ntly less virulent than wild-type virus separates the spontaneous reac tivation phenotype from the virulence phenotype.