Two overlapping transcription units which extend across the L-S junction of herpes simplex virus type 1

Abstract

A region of the herpes simplex virus type 1 genome located upstream of the ␣0 promoter contains a promoter which regulates transcription in the opposite orientation to that driven by ␣0. Analyses of mutants from which this promoter, ␣X, was deleted and a mutant in which a fragment that serves as a transcription terminator and polyadenylation signal was inserted upstream of this promoter demonstrate that two distinct transcription units overlap this region of the genome and are transcribed in a direction antisense to the neurovirulence gene ␥ 1 34.5. One unit, dependent on the ␣X promoter, is active when cells are infected in the presence of the protein synthesis inhibitor cycloheximide. The second unit, independent of ␣X, is active during the course of productive infection. This transcription unit originates from a promoter upstream of ␣X which is distinct from the latency-associated promoter (LAP). Two polyadenylated transcripts of 0.9 and 4.9 kb accumulate from this region of the genome during productive infection, but no mature transcripts accumulate in infected cells maintained in the presence of cycloheximide. Kinetic analyses demonstrate that the transcripts that accumulate during productive infection fall into the ␤ class of herpes simplex virus type 1 genes.

The spontaneous reactivation function of the herpes simplex virus type 1 LAT gene resides completely within the first 1.5 kilobases of the 8.3-kilobase primary transcript

“…Recently, an HSV-1 RNA that is colinear and coterminal with approximately the last 25% of the primary 8.3-kb LAT has been described (3,16,17,46). This RNA is transcribed independently of LAT, contains a presumptive open reading frame (ORF P), and appears to be made in tissue culture under some circumstances.…”

A novel herpes simplex virus 1 gene, UL43.5, maps antisense to the UL43 gene and encodes a protein which colocalizes in nuclear structures with capsid proteins

“…(v) In recent years, a number of new genes that were not predicted by analysis of the genomic sequence have been identified in the HSV-1 genome (5,7,9,10,16,18,19,23). In addition, there is accumulating evidence that genes may be either required in some cells but not others (e.g., U L 20) or expressed (e.g., ORF P) under unusual regulatory conditions and therefore whose products may not be readily detected (8,18,34). The precise function of U L 43.5 may emerge from studies on experimental infected cell environments in which its role is essential and affects viral replication in a quantifiable fashion.…”

Experimental investigation of herpes simplex virus latency

“…Similarly, the ORF-P protein expressed from one or another low-abundance transcripts which are partially colinear but independently controlled by productive-phase promoters (Fig. 1) does not seem to play any measurable role in the reactivation process (17,21,145,189).…”

“…One of the problems with attempting to work with such low-abundance transcripts is that no biological function related to the expression of LAT maps to the regions identified. Another major problem is that there are a number of productivephase, low-abundance transcripts mapping within the contiguous limits of the LAT unit whose kinetics of expression and regulation are unusual in that they are inhibited by immediateearly transcription (21,322). Such transcripts can greatly complicate the analysis of low-abundance transcripts thought to be associated with latent infection, since much of the analysis must be done in cultured cells.…”