Initiation of transcription and RNA synthesis, processing and transport in HSV and VZV infected cells

Excerpt

During productive infection by herpes simplex virus type 1 (HSV-1), approximately 80 genes encoded within the linear 152-kbp viral genome are expressed in three sequential phases that are termed immediate early (IE; α), early (E; β) and late (L; γ)(Honess and Roizman, ; McGeoch, 1991). The smaller, 125-kbp varicella zoster virus (VZV) genome encodes around 70 genes, which are also expressed as IE, E and L products (Davison and Scott, 1986). HSV -1 and VZV genes are transcribed by the cellular RNA Polymerase Ⅱ and each viral promoter has a TATA box homology about 25 nucleotides upstream of the start site of transcription (for review, see Wagner et al., 1995). In HSV -1infections, the first genes to be transcribed are the five IE genes, which are distinguished from E and L genes by specific sequence elements termed TAATGARAT sequences in the upstream regions of IE promoters. These elements are recognized by a virion tegument protein, VP 16, which binds as part of a protein complex that contains two cellular factors, Oct-1 and HCF, to transcriptionally activate expression of IE genes (Wysocka and Herr, 2003). VZV IE genes do not appear to encode upstream promoter elements similar to the TAATGARAT sequence, however VZV does encode a protein, ORF 10 that exhibits similarities with VP 16, although its activity has been much less well characterized than that of VP 16 (Piette et al., 1995).