Abstract
Varicella-zoster virus (VZV) open reading frame 10 (ORF10) protein, the homolog of herpes simplex virus type 1 (HSV-1) VP16, is a virion-associated transactivator of the VZV immediate-early (IE) gene 62 (IE62) promoter. VP16 forms a complex with cellular factors (Oct1 and host cell factor [HCF]) and TAATGARAT elements (found in all HSV-1 IE promoter/enhancer sequences) to mediate stimulation of IE transcription. The VZV IE62 promoter also contains three TAATGARAT-like elements. Mutagenesis studies of the VZV IE62 promoter indicated that TAATGARAT-like elements contribute to transactivation of the VZV IE62 promoter by ORF10 protein. Other cis-acting elements such as GA-rich and cyclic AMP-responsive elements were also needed for full transactivation by ORF10 protein. In mobility shift assays, ORF10 protein formed a complex with either of two TAATGARAT-like elements that lack an overlapping octamer-binding motif (octa-/TAATGARAT) but not with a TAATGARAT element with an overlapping octamer-binding motif (octa+/TAATGARAT). In contrast, VP16 formed a high-affinity ternary complex with an octa+/TAATGARAT element and a low-affinity complex with octa-/TAATGARAT elements. Addition of antibodies to ORF10 protein, Oct1, or HCF disrupted the complexes, demonstrating that ORF10 protein interacts with Oct1 and HCF. These results suggest that transactivation of the VZV IE62 gene by ORF10 protein and HSV IE genes by VP16 require similar cellular proteins but distinct cis-acting elements.