title: The envelope G3L protein is essential for entry of vaccinia virus into host cells.
abstract: The vaccinia virus G3L/WR079 gene encodes a conserved protein with a predicted transmembrane domain. Our proteomic analyses of vaccinia virus revealed that G3L protein is incorporated into intracellular mature virus; however, the function of G3L protein in the vaccinia virus life cycle has not been investigated. In this study, a recombinant vaccinia virus, viG3L, expressing G3L protein under IPTG (isopropyl-beta-d-thiogalactopyranoside) regulation was constructed. Under permissive conditions when G3L protein was expressed, the vaccinia virus life cycle proceeded normally, resulting in plaque formation in BSC40 cells. In contrast, under nonpermissive conditions when G3L protein expression was repressed, no plaques were formed, showing that G3L protein is essential for vaccinia virus growth in cell cultures. In infected cells when G3L protein was not expressed, the formation of intracellular mature virus (IMV) and cell-associated enveloped virus occurred normally, showing that G3L protein is not required for virion morphogenesis. IMV particles containing (G3L(+)) or lacking (G3L(-)) G3L protein were purified and were found to be indistinguishable on microscopic examination. Both G3L(+) and G3L(-) IMV bound to HeLa cells; however, G3L(-) IMV failed to enter the cells, showing that G3L protein is required for IMV penetration into cells. Finally, G3L protein was required for fusion of the infected cells under low-pH treatment. Thus, our results provide direct evidence that G3L is an essential component of the vaccinia virus fusion complex, in addition to the previously reported A28, H2, L5, A21, and A16 proteins.
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.
authors.forename: Ruzan A
authors.initials: RA
authors.lastname: Izmailyan
authors.forename: Cheng-Yen
authors.initials: CY
authors.lastname: Huang
authors.forename: Shamim
authors.initials: S
authors.lastname: Mohammad
authors.forename: Stuart N
authors.initials: SN
authors.lastname: Isaacs
authors.forename: Wen
authors.initials: W
authors.lastname: Chang
mesh_terms: D000595:Amino Acid Sequence; D002459:Cell Fusion; D002460:Cell Line; D015967:Gene Expression Regulation, Viral; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D014616:Vaccinia virus / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010948:Viral Plaque Assay; D014771:Virion / Q000378:metabolism
chemical_list: D014759:Viral Envelope Proteins