The Initiator Element in a Herpes Simplex Virus Type 1 Late-Gene Promoter Enhances Activation by ICP4, Resulting in Abundant Late-Gene Expression

Abstract

The start site regions of late genes of herpes simplex virus type 1 are similar to the eukaryotic initiator sequence (Inr), have been shown to affect the levels of expression, and may also play a role in transcription activation by the viral activator ICP4. A series of linker-scanning mutations spanning the start site of transcription and several downstream mutations in the true late gC promoter were analyzed in reconstituted in vitro transcription reactions with and without ICP4, as well as in the context of the viral genome during infection. The nucleotide contacts previously found to be important for Inr function were also found to be important for optimal induction by ICP4. While the Inr had a substantial effect on the accumulation of gC RNA during infection, no other sequence downstream of the TATA box to ؉124 had a significant effect on levels of expression during infection. Therefore, these studies suggest that TATA box and the Inr are the only cis-acting elements required to achieve optimal expression of gC, and that the high levels of late-gene transcription may be largely due to the induction by ICP4, functioning through the Inr element.During productive infection by herpes simplex virus type 1 (HSV-1), approximately 80 genes are sequentially expressed in three major kinetic groups: immediate-early (IE, ␣), early (E, ␤), and late (L, ␥) genes (36,37,46,60,61). Each HSV-1 gene has its own promoter with an obvious TATA box homology that is recognized by the host RNA polymerase II transcription machinery (1,11,89). A viral protein VP16, carried in with the virion, activates transcription of the five IE genes in a complex with two cellular proteins, Oct-1 and HCF (5,55,66). Once expressed, the IE gene products regulate expression of the early and late genes by a variety of mechanisms in the course of infection (75).One of the IE proteins, ICP4 (infected-cell polypeptide 4), is essential for viral growth as it is required for optimal expression of most early and late genes (15,19,22,25,67,68). ICP4 is a nuclear phosphoprotein that acts as a homodimer to activate or repress transcription depending upon the promoter (12,15,26,54,63,67,71). Genetic and biochemical studies have shown that ICP4 binds to DNA and interacts with a component(s) of general RNA polymerase II transcription machinery to activate or repress transcription (2,8,17,29,42,64,65,84). ICP4 forms a tripartite complex with TFIIB and TATA binding protein (TBP) on DNA, interacts with TBP-associated factor 250 (8, 84), and promotes the formation of transcription preinitiation complexes on promoters (28).The transcriptional regulation of HSV genes during infection is mostly determined by the structure of a given promoter. The promoters of IE and E genes contain a number of cisacting elements upstream of the TATA box (89, 90). Viral and cellular proteins (Oct-1/VP16, Sp1, CTF or NF1, etc.) bind to these cis-acting elements to activate transcription (21,24,25,45,89). An important characteristic of late genes is that their expression is significantly i...

Transcriptional analysis of the white spot syndrome virus major virion protein genes

“…For proper late gene expression of large dsDNA viruses, the motif that contains the TIS is often an important viral promoter element. Mutations in the late motif TAAG of baculoviruses (Morris & Miller, 1994), the late TAAAT motif of poxviruses (Davison & Moss, 1989), the TATA initiator of ASFV (Garcia-Escudero & Viñuela, 2000) and the more diverged initiator YYANWYY (N=any nucleotide; W=t/a) of herpesviruses (Kim et al, 2002;Weir, 2001) often lead to a (dramatic) downregulation of gene expression. The 59 RACE analyses indicate that transcription of the WSSV genes vp28, vp26, vp24, vp19 and vp15 did not start at a consensus sequence for all five genes (Fig.…”

“…Immediate early (IE) and early (E) genes are expressed before viral DNA replication, while expression of late (L) genes occurs after replication of the viral genome. For proper late gene expression, the motif that contains the transcription initiation site (TIS) often plays a prominent role in recognition by a virus-coded RNA polymerase (Davison & Moss, 1989;Garcia-Escudero & Viñuela, 2000;Kim et al, 2002;Morris & Miller, 1994;Weir, 2001). Information about pathogenicity, epidemiology, virion structure and the genomic sequence of WSSV is now available, but insight into gene regulation is limited.…”

The Human Cytomegalovirus Gene UL79 Is Required for the Accumulation of Late Viral Transcripts

“…In HSV, DNA replication is required in cis for activity of late promoters (26,34). HSV proteins, including ICP4, ICP8, and ICP27, are necessary for efficient expression of late genes by interacting with the general transcription machinery (19,28,47), and they facilitate the assembly of transcription preinitiation complexes (8,65). In MHV-68, both viral DNA replication (12) and four viral proteins, ORF18, ORF24, ORF30, and ORF34, are required for late gene expression (2, 60, 61).…”

The function of temporally ordered viral gene expression in the intracellular replication of herpes simplex virus type 1 (HSV-1)

“…The expressions of both early and late genes are regulated by the immediate early gene product such as ICP4 (Kim et al, 2002). The temporally ordered expression of early and late genes is controlled by the difference in the structure of their promoters.…”