title: Assembly of nucleocapsids with cytosolic and membrane-derived matrix proteins of vesicular stomatitis virus.
abstract: During budding of vesicular stomatitis virus (VSV), the viral matrix (M) protein binds the viral nucleocapsid to the host plasma membrane and condenses the nucleocapsid into the tightly coiled nucleocapsid-M protein (NCM) complex observed in virions. In infected cells, the viral M protein exists mostly as a soluble molecule in the cytoplasm, and a small amount is bound to the plasma membrane. Despite the high concentrations of M protein and intracellular nucleocapsids in the cytoplasm, they are not associated with each other except at the sites of budding. The experiments presented here address the question of why M protein and nucleocapsids associate with each other only at the plasma membrane but not in the cytoplasm of infected cells. An assay for exchange of soluble M protein into NCM complexes in vitro was used to show that both cytosolic and membrane-derived M proteins bound to virion NCM complexes with affinities similar to that observed for virion M protein, indicating that both cytosolic and membrane-derived M proteins are competent for virus assembly. However, neither cytosolic nor membrane-derived M protein bound to intracellular nucleocapsids with the same high affinity observed for virion NCM complexes. Cytosolic M protein was able to bind intracellular nucleocapsids, but with an affinity approximately eightfold less than that observed in virion NCM complexes. Membrane-derived M protein exhibited little or no binding activity for intracellular nucleocapsids. These data indicate that intracellular nucleocapsids, and not intracellular M proteins, need to undergo an assembly-initiating event in order to assemble into an NCM complex. Since neither membrane-derived nor cytosolic M protein could initiate high-affinity binding to intracellular nucleocapsids, the results suggest that another viral or host factor is required for assembly of the NCM complex observed in virions.
authors.affiliation: Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1064, USA. eflood@wfubmc.edu
authors.forename: E A
authors.initials: EA
authors.lastname: Flood
authors.forename: D S
authors.initials: DS
authors.lastname: Lyles
mesh_terms: D000818:Animals; D002213:Capsid / Q000502:physiology*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D014721:Vesicular stomatitis Indiana virus / Q000502:physiology*; D014763:Viral Matrix Proteins / Q000502:physiology*; D019065:Virus Assembly
chemical_list: D014763:Viral Matrix Proteins