The Product of Gene US11 of Herpes Simplex Virus Type 1 Is Expressed as a True Late Gene

Abstract

SUMMARYThe genes of herpes simplex virus type 1 (HSV-1) can be divided into at least three temporally regulated groups termed immediate early (IE), early and late. We have Studied in detail the expression of a member of the late class of genes, US11, which encodes a polypeptide of apparent molecular weight 21K. Highly specific and sensitive probes were used to monitor US1 t RNA and protein synthesis during HSV-1 infection of tissue culture cells in the presence and absence of phosphonoacetic acid, an inhibitor of viral DNA replication. The results were compared with a similar study of the products of a delayed early gene, US6, encoding glycoprotein D (gD). It was found that the patterns of RNA and protein synthesis from US11 were significantly different to those of gD. US11 products appeared later and accumulated until late in infection, while gD RNA was significantly reduced at late times. In the presence of the inhibitor of DNA synthesis, USll gene expression was reduced 50-to 100-fold while gD expression was reduced five-to tenfold. We conclude that US11 behaves as a true late gene during HSV-1 infection. However, the use of sensitive assays, which allowed the detection of very low levels of USI 1 gene products under conditions designed to eliminate DNA replication, brings into question the absolute requirement for DNA replication for the expression of a true late HSV-1 gene. These results are discussed in terms of current models for the regulation of late gene expression.

Identification and Characterization of the Virion Protein Products of Herpes Simplex Virus Type 1 Gene UL47

“…This finding is exactly what would be expected for true late proteins and essentially parallels the result with 21K (b), previously found to be a true late protein (Johnson et al, 1986). In contrast, 65KDBp is clearly detectable by 6 h post-infection and is only slightly inhibited by PAA in the wild-type virus-infected cells (c).…”

“…To determine whether gene UL47 was regulated as a true late gene according to this definition, the expression of the 82K protein was examined in the presence of 300 ~tg/ml PAA. At this concentration, virus DNA replication is reduced to undetectable levels (< 5~o of the no drug control) in cells infected with HSV-1 strain 17 (Johnson et al, 1986). The PAA-resistant mutant, PAAr-1, (Hay & Subak-Sharpe, 1976), which induces wild-type levels of virus DNA synthesis in the presence of 300 p.g/ml PAA, was included in the experiment as a control.…”

“…This dramatic up-regulation was reproducibly observed and suggests that gene UL47 is regulated as a late gene. Johnson et al (1986) suggested an operational definition of true late genes as those whose expression is most severely reduced, compared to all other groups of genes, under conditions of severely inhibited virus DNA replication. To determine whether gene UL47 was regulated as a true late gene according to this definition, the expression of the 82K protein was examined in the presence of 300 ~tg/ml PAA.…”

“…The PAA-resistant mutant, PAAr-1, (Hay & Subak-Sharpe, 1976), which induces wild-type levels of virus DNA synthesis in the presence of 300 p.g/ml PAA, was included in the experiment as a control. For comparison, the behaviour of two other proteins was also examined: 21K, a true late protein (Johnson et al, 1986) and 65KDBP, an early protein (Schenk & Ludwig, 1988;Goodrich et al, t989) whose synthesis is reduced three-to four-fold in the presence of PAA (Goodrich et al, 1989). The reactivities on Western blots of the rabbit antisera 18826 and 14327 when used to detect expression of 65KDBp and 21K respectively have previously been described (Parris et al, 1988;MacLean et al, 1987).…”

“…Evidence exists for nine true late mRNAs (Holland et al, 1980, I984;Frink et al, Hall et al, 1982;Silver & Roizman, 1985;Johnson et al, 1986). Comparison of the positions and sizes of these transcripts with the DNA sequence obtained by McGeoch et al (1988) suggests that these true late mRNAs may originate from genes UL22, UL31, UL32, UL38, UL44, UL45, UL47, UL49 and US11, but quantitative data for mRNA regulation has been obtained only for UL49 (Silver & Roizman, 1985) and US11 (Johnson et al, 1986). Quantitative data will have to be obtained for the others to identify these genes unambiguously as true late.…”