THE ENVELOPE PROTEIN ENCODED BY THE A33R GENE IS REQUIRED FOR FORMATION OF ACTIN-CONTAINING MICROVILLI AND EFFICIENT CELL-TO-CELL SPREAD OFVACCINIA VIRUS

Citation
Rl. Roper et al., THE ENVELOPE PROTEIN ENCODED BY THE A33R GENE IS REQUIRED FOR FORMATION OF ACTIN-CONTAINING MICROVILLI AND EFFICIENT CELL-TO-CELL SPREAD OFVACCINIA VIRUS, Journal of virology, 72(5), 1998, pp. 4192-4204
Citations number
58
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Virology
Journal title
ISSN journal
0022-538X
Volume
72
Issue
5
Year of publication
1998
Pages
4192 - 4204
Database
ISI
SICI code
0022-538X(1998)72:5<4192:TEPEBT>2.0.ZU;2-P
Abstract
The vaccinia virus (VV) A33R gene encodes a highly conserved 23- to 28 -kDa glycoprotein that is specifically incorporated into the viral out er envelope. The protein is expressed early and late after infection, consistent with putative early and late promoter sequences. To determi ne the role of the protein, two inducible A33R mutants were constructe d, one with the late promoter and one with the early and late A33R pro moter elements. Decreased A33R expression was associated with small pl aques that formed comets in liquid medium. Using both an antibiotic re sistance gene and a color marker, an A33R deletion mutant, vA33 Delta, was isolated, indicating that the A33R gene is not essential for VV r eplication. The plaques formed by vA33 Delta, however, were tiny, indi cating that the A33R protein is necessary for efficient cell-to-cell s pread. Rescue of the large-plaque phenotype was achieved by inserting a new copy of the A33R gene into the thymidine kinase locus, confirmin g the specific genetic basis of the phenotype. Although there was a re duction in intracellular virus formed in cells infected with vA33 Delt a, the amount of infectious virus in the medium was increased. The vir us particles in the medium had the buoyant density of extracellular en veloped viruses (EEV). Additionally, amounts of vA33 Delta cell-associ ated extracellular enveloped viruses (CEV) were found to be normal. Im munogold electron microscopy of cells infected with vA33 Delta demonst rated the presence of the expected F13L and B5R proteins in wrapping m embranes and EEV; however, fully wrapped vA33 Delta intracellular enve loped viruses (IEV) were rare compared to partially wrapped particles. Specialized actin tails that propel IEV particles to the periphery an d virus-tipped microvilli (both common in wild-type-infected cells) we re absent in cells infected with vA33 Delta. This is the first deletio n mutant in a VV envelope gene that produces at least normal amounts o f fully infectious EEV and CEV and yet has a small-plaque phenotype. T hese data support a new model for VV spread, emphasizing the importanc e of virus-tipped actin tails.