A 371-NUCLEOTIDE REGION BETWEEN THE HERPES-SIMPLEX VIRUS TYPE-1 (HSV-1) LAT PROMOTER AND THE 2-KILOBASE LAT IS NOT ESSENTIAL FOR EFFICIENT SPONTANEOUS REACTIVATION OF LATENT HSV-1

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) gene is essential for efficient spontaneous reactivation of HSV- 1 from latency, However, neither the mechanism by which LAT carries ou t this function nor the region of LAT responsible for this function is known. LAT is transcribed as an unstable 8.3-kb RNA that gives rise t o a very stable 2-kb LAT RNA that is readily detected in latently infe cted sensory neurons. We show here that 371 of the 662 nucleotides loc ated between the start of LAT transcription and the 5' end of the 2-kb LAT RNA do not appear to he essential for wild-type levels of spontan eous reactivation in the rabbit ocular model of HSV-1 latency. We dele ted LAT nucleotides 76 to 447 from both copies of the LAT gene (one in each viral long repeat) to produce the mutant dLAT371. Rabbits were o cularly infected with dLAT371, and spontaneous reactivation was measur ed in comparison with the marker-rescued virus dLAT371R. Both dLAT371 and dLAT371R had spontaneous reactivation rates of approximately 13 to 14%. This was consistent with the parental McKrae wild-type virus (11 .7%; P = 0.49) and significantly higher than the LAT transcription-neg ative mutant dLAT2903 (2.4%; P < 0.0001). Southern analysis confirmed that the spontaneously reactivated dLAT371 virus retained the deletion in both copies of LAT. Therefore, it appeared that the function of LA T involved in efficient spontaneous reactivation mapped outside the 37 1-nucleotide region deleted from the LAT gene of dLAT371.