The latency-associated promoter of herpes simplex virus type 1 requires a region downstream of the transcription start site for long-term expression during latency

The latency-associated transcript (LAT) promoter of herpes simplex virus type 1 (HSV-1) is unique among the many promoters on the viral genome in that it remains active during the latent state. We have previously shown that a DNA fragment comprising the LAT promoter element through the cap site, when moved from the LAT locus to the glycoprotein C gene, is capable of only short-term expression. These and other data suggested that an HSV DNA element from the repeat region, not included in the LAT promoter itself, might be needed to preserve long-term expression. Based on a number of recombinant viruses, we narrowed our search for this putative element to a region 3' of the LAT transcription start site. In the present study, we have shown that a 1.1-kb DNA fragment containing the putative long-term expression element (LTE) is able to restore latent-phase gene expression to the LAT promoter. The element appeared to function best when it was placed in its natural location, which is 3' of the LAT promoter; however, partial function was obtained when the LTE was inserted upstream of the LAT promoter in the reverse direction. These data indicate that the LAT promoter region is more complex than originally anticipated and that in addition to requiring both core promoter and neuronal transcription factor binding sites, the promoter requires a specific region of DNA to prevent its shutoff during a latent infection.</jats:p

Cloning, sequencing, and functional characterization of the two subunits of the pseudorabies virus DNA polymerase holoenzyme: evidence for specificity of interaction

The pseudorabies virus (PRV) genes encoding the two subunits of the DNA polymerase were located on the genome by hybridization to their herpes simplex virus type 1 (HSV-1) homologs, pol and UL42, and subsequently were sequenced. Like the HSV-1 homologs, in vitro translation products of the PRV gene encoding the catalytic subunit (pol) possessed activity in the absence of the Pol accessory protein (PAP). However, the PRV PAP stimulated the activity of Pol fourfold in the presence of 150 mM KCl, using an activated calf thymus DNA template. The stimulation of Pol activity by PAP under high-salt conditions and the inhibition of Pol activity by PAP when assayed in low salt (0 mM KCl) together were used to determine the specificity with which PAP interacted with Pol. Despite functional similarity, HSV-1 UL42 and PRV PAP could neither stimulate the noncognate Pols at high salt nor inhibit them at low salt. Furthermore, a PRV Pol mutant lacking the 30 C-terminal amino acids retained basal Pol activity but could be neither stimulated nor inhibited by the PRV PAP. Sequence comparisons of the Pol proteins of the alphaherpesviruses reveal a conserved domain in the C terminus which terminates immediately before the last 41 residues of both PRV and HSV-1 proteins. These results indicate that the ability and specificity for interaction of the PRV Pol with PAP most likely resides predominantly in the extreme Pol C terminus.</jats:p

Herpes Simplex Virus Virion Host Shutoff Protein Requires a Mammalian Factor for Efficient In Vitro Endoribonuclease Activity

The virion host shutoff protein (vhs) of herpes simplex virus (HSV) triggers global shutoff of host protein synthesis and accelerated mRNA turnover during virus infection and induces endoribonucleolytic cleavage of exogenous RNA substrates when it is produced in a rabbit reticulocyte (RRL) in vitro translation system. Although vhs induces RNA turnover in the absence of other HSV gene products, it is not yet known whether cellular factors are required for its activity. As one approach to addressing this question, we expressed vhs in the budding yeast Saccharomyces cerevisiae. Expression of vhs inhibited colony formation, and the severity of this effect varied with the carbon source. The biological relevance of this effect was assessed by examining the activity of five mutant forms of vhs bearing previously characterized in-frame linker insertions. The results indicated a complete concordance between the growth inhibition phenotype in yeast and mammalian host cell shutoff. Despite these results, expression of vhs did not trigger global mRNA turnover in vivo, and cell extracts of yeast expressing vhs displayed little if any vhs-dependent endoribonuclease activity. However, activity was readily detected when such extracts were mixed with RRL. These data suggest that the vhs-dependent endoribonuclease requires one or more mammalian macromolecular factors for efficient activity