Transcript mapping and transregulatory behavior of varicella-zoster virus gene 21, a latency-associated gene

Gene 21 is one of at least four genes transcribed during latent infection of varicella-zoster virus (VZV) in human ganglia. It may encode a nucleocapsid protein, but its function in lytic and latent infection is not clear. To characterize further the structure and the function of the gene 21 open reading frame (ORF 21), precise localization of its transcripts and their termini was determined by using Northern analysis, S1 nuclease or RNase protection, and primer extension assays. One abundant 3.5-kb transcript that spans ORF 21 was identified. A predominant transcription start site was defined at -78 nucleotide (nt) relative to the ORF 21 translation start codon ATG, and two potential TATA elements were identified at 26 and 83 nt upstream of the 5' end of gene 21 transcripts. Transcription was found to terminate 210 nt beyond the ORF 21 translation stop codon and immediately before the start codon of ORF 22. In transient expression assays, the ORF 21 showed no significant transregulatory activity on promoters of diverse kinetic classes. The ORF 21 promoter, however, was transactivated strongly by VZV infection or by ORF 62.