Two herpes simplex virus type 1 latency-active promoters differ in their contributions to latency-associated transcript expression during lytic and latent infections

Abstract

Herpes simplex virus type 1 (HSV-1) establishes latency in human sensory ganglia, during which time the viral genome is transcriptionally silent with the exception of the latency-associated transcripts (LATs). The most abundant LAT is a 2-kb RNA whose biosynthesis is poorly characterized. The 2-kb LAT may be a primary transcript, or its synthesis may involve splicing and/or other forms of processing. Two potential RNA polymerase II promoters (LAP1 and LAP2) upstream of the 2-kb LAT 5 end have been identified. To investigate the role played by LAP1 and LAP2 in the synthesis of the 2-kb LAT under lytic and latent conditions, we analyzed HSV-1 mutants which contain deletions of one or both of these promoters. During lytic infection in cell culture, the cis elements critical for the normal accumulation of the 2-kb LAT were mapped to LAP2, while LAP1 sequences were largely dispensable. The 5 ends of the major 2-kb LATs produced by the wild-type and LAP deletion viruses were examined by primer extension analysis and were all found to be identical (؎2 bp). The accumulation of the 2-kb LAT during latent infections of murine trigeminal ganglia was examined by Northern (RNA) blot and by reverse transcription-PCR. In contrast to the results found in lytic infections, the critical cis elements needed for 2-kb LAT accumulation during latency were mapped to LAP1. Deletion of LAP1 resulted in a 500-fold reduction in 2-kb LAT accumulation, whereas deletion of LAP2 resulted in only a 2-to 3-fold reduction. Deletion of both LAP1 and LAP2 resulted in undetectable levels of the 2-kb LAT. Our results indicate that both LAP1 and LAP2 are critical for 2-kb LAT expression but under different conditions. LAP1 is essential for LAT expression during latency, while LAP2 is primarily responsible for LAT expression in lytic infections in cell culture. LAP1 and LAP2 may prove to be functionally independent promoter elements that control 2-kb LAT expression during different stages of HSV-1 infections.

Prevalence of HSV‐1 LAT in Human Trigeminal, Geniculate, and Vestibular Ganglia and Its Implication for Cranial Nerve Syndromes

“…A low accumulation of LAT suggests the presence of a distinctive mechanism that regulates and processes LAT in the neurons of the VG. This agrees with findings of recent studies that LAT synthesis differs in certain neurons depending on the host transcription factors (7,33). Moreover, a smaller amount of LAT and a different processing method could influence the pathophysiology and clinical manifestation of a reactivation in the VG.…”

Experimental investigation of herpes simplex virus latency

“…Although deletions of the latent phase promoter abolish readily measurable transcription during latent infection as assayed by in situ hybridization and PCR analysis (16,30,(55)(56)(57)60), some workers continue to speculate about the existence of a second latent phase promoter just upstream of the splice acceptor region of the stable 2-kb intron. This speculation is based on the following observations.…”

Human Herpes Viruses Latent Infection in the Nervous System

“…The transcription present during latency consists of two, more abundant latency-associated transcripts (LAT) 2.0 and 1.5 kb in size, and transcripts that are present in smaller amounts, about 8.4 kb in size, termed the minor LAT (mLAT). Two promoters of this gene (latency-active promoters; LAP), LAP-1 and LAP-2, have been mapped (Nicosia et al 1993, Goins et al 1994, Chen et al 1995. While LAP-1 is more active during latent in vivo infection and LAP-2 is more active during viral replication in cells in culture, both are probably required for effective latent infection.…”