Transcriptional mapping of the varicella-zoster virus regulatory genes encoding open reading frames 4 and 63

Abstract

Four of the 68 varicella-zoster virus (VZV) unique open reading frames (ORFs), i.e., ORFs 4, 61, 62, and 63, encode proteins that influence viral transcription and are considered to be positional homologs of herpes simplex virus type 1 (HSV-1) immediate-early (IE) proteins. In order to identify the elements that regulate transcription of VZV ORFs 4 and 63, the encoded mRNAs were mapped in detail. For ORF 4, a major 1.8-kb and a minor 3.0-kb polyadenylated [poly(A)+] RNA were identified, whereas ORF 63-specific probes recognized 1.3- and 1.9-kb poly(A)+ RNAs. Probes specific for sequences adjacent to the ORFs and mapping of the RNA 3' ends indicated that the ORF 4 RNAs were 3' coterminal, whereas the RNAs for ORF 63 represented two different termination sites. S1 nuclease mapping and primer extension analyses indicated a single transcription initiation site for ORF 4 at 38 bp upstream of the ORF start codon. For ORF 63, multiple transcriptional start sites at 87 to 95, 151 to 153, and (tentatively) 238 to 243 bp upstream of the ORF start codon were identified. TATA box motifs at good positional locations were found upstream of all mapped transcription initiation sites. However, no sequences resembling the TAATGARAT motif, which confers IE regulation upon HSV-1 IE genes, were found. The finding of the absence of this motif was supported through analyses of the regulatory sequences of ORFs 4 and 63 in transient transfection assays alongside those of ORFs 61 and 62. Sequences representing the promoters for ORFs 4, 61, and 63 were all stimulated by VZV infection but failed to be stimulated by coexpression with the HSV-1 transactivator Vmw65. In contrast, the promoter for ORF 62, which contains TAATGARAT motifs, was activated by VZV infection and coexpression with Vmw65. These results extend the transcriptional knowledge for VZV and suggest that ORFs 4 and 63 contain regulatory signals different from those of the ORF 62 and HSV-1 IE genes.