Localization of Varicella-Zoster Virus Gene 21 Protein in Virus-Infected Cells in Culture

Abstract

Although four varicella-zoster virus (VZV) genes have been shown to be transcribed in latently infected human ganglia, their role in the development and maintenance of latency is unknown. To study these VZV transcripts, we decided first to localize their expression products in productively infected cells. We began with VZV gene 21, whose open reading frame (ORF) is 3,113 bp. We cloned the 5′ and 3′ ends and the predicted antigenic segments of the ORF as 1292-, 1280-, and 880-bp DNA fragments, respectively, into the prokaryotic expression vector pGEX-2T. The three VZV 21 ORFs were expressed as approximately 75-, 73-, and 59-kDa glutathione S-transferase fusion proteins in Escherichia coli. To prepare polyclonal antibodies that would recognize all potential epitopes on the VZV gene 21 protein, rabbits were inoculated with a mixture of the three fusion proteins, and antisera were obtained and affinity purified. Immunohistochemical and immunoelectron microscopic analyses using these antibodies revealed VZV ORF 21 protein in both the nucleus and cytoplasm of VZV-infected cells. When these antibodies were applied to purified VZV nucleocapsids, intense staining was seen in their central cores.

Latency of varicella zoster virus a persistently perplexing state

“…Regarding ORF21, very little is known about its functions. In acutely infected cells the protein is present in both the cytoplasm and the nucleus, and appears to be tightly associated with the nucleocapsid (112). Its HSV-1 homolog, UL37, is expressed as a late gene, and encodes a bifunctional protein that co-operates with the DNA binding protein from ICP8 on single-stranded DNA affinity columns (84).…”