Varicella-zoster virus ORF1 gene product is a tail-anchored membrane protein localized to plasma membrane and trans-Golgi network in infected cells

Abstract

Varicella-zoster virus (VZV) encodes five genes that do not have herpes simplex virus homologs. One of these genes, VZV open reading frame 1 (ORF1), encodes a membrane protein with a hydrophobic domain at its C-terminus that is predicted to be the transmembrane domain. However, the detailed characterization of ORF1 protein in infected cells has not been reported. Here, we produced mono-specific antibodies against ORF1 protein and characterized the gene products in infected cells. Western blot analyses showed the ORF1 polypeptides had apparent molecular masses of approximately 14–17 kDa. Furthermore, ORF1 was found to be a phosphoprotein by immunoprecipitation assay. In immunofluorescence assays, the VZV ORF1 protein was detected at both the plasma membrane and trans-Golgi network in both VZV-infected and ORF1-transfected cells. Moreover, ORF1 proteins associated with each other to form homodimer, and were incorporated into viral particles. The C-terminal hydrophobic domain was required for the association of ORF1 with the membrane structures, indicating that ORF1 protein is anchored to the membrane thorough its C-terminus, which is a transmembrane domain. Because ORF1 possesses a C-terminal transmembrane domain without an N-terminal signal sequence for its translocation to the ER lumen, ORF1 can be classified as a tail-anchored membrane protein. These results show that the N terminus of ORF1 protein faces the cytoplasm in infected cells and the tegument region in mature virions.