Herpes simplex virus type 1 latency-associated transcripts are evidently not essential for latent infection.

The herpes simplex virus type 1 (HSV-1) transcripts that can be detected during latent infection by Northern blot analysis in human and experimental animal sensory ganglia are encoded by diploid genes. To investigate their role in latent infection we studied HSV-1 variant 1704, which has deleted most of the IRL copy of the coding region of these RNAs and has a 1.2-kb deletion that is immediately upstream of the coding region of the TRL copy. During primary infection, 1704 replicated in trigeminal ganglia with kinetics similar to the parent virus (17+) and established latent infection. However, while explant reactivation of latent HSV-1 from trigeminal ganglia was detected in 100% of 17+ infected mice within 7 days, the reactivation of 1704 was significantly delayed, and 31 days elapsed before eight out of nine mice became virus positive. The recognized HSV-1 latency-associated RNAs were not detected during the latent state of 1704 by Northern blot analysis or in situ hybridization, which implies that the 1.2-kb deletion may contain the promoter or other important regulatory elements. The data indicate that detectable levels of these latency-associated transcripts are not required for viral replication, establishment, or maintenance (greater than 6 weeks) of HSV-1 latency in trigeminal ganglia, but suggest a role in reactivation.