Role of ribosomes in Semliki Forest virus nucleocapsid uncoating

Abstract

The mechanism by which Semliki Forest virus nucleocapsids are uncoated was analyzed in living cells and in vitro. In BHK-21 cells, uncoating occurred with virtually complete efficiency within 1 to 2 min after the nucleocapsids entered the cytoplasm. It was inhibited by monensin, which blocks nucleocapsid penetration from endosomes. As previously shown for Sindbis virus (G. Wengler and G. Wengler, Virology 134:435-442, 1984), the capsid proteins from incoming nucleocapsids became associated with ribosomes. The ribosomebound capsid proteins were distributed throughout the cytoplasm, while the viral RNA remained associated with vacuolar membranes. Using purified nucleocapsids and ribosomes in vitro, we established that ribosomes alone were sufficient for uncoating. Their role was to release the capsid proteins from nucleocapsids and irreversibly sequester them, in a process independent of energy and translation. The process was stoichiometric rather than catalytic, with a maximum of three to six capsid proteins bound to each ribosome. More than 80%o of the capsid proteins could thus be removed from the viral RNA, resulting in the formation of nucleocapsid remnants whose sedimentation coefficients progressively decreased from 140S to 80S as uncoating proceeded.

Identification of Interactions between Sindbis Virus Capsid Protein and Cytoplasmic vRNA as Novel Virulence Determinants

“…Several studies have described interactions between the alphaviral capsid protein and host ribosomal RNAs. Indeed, co-sedimentation studies indicated that the host 60S rRNAs interact with viral capsid proteins in vertebrate cells during infection [65,66]. This interaction has been proposed to be a leading mechanism in particle disassembly [66].…”

Mechanisms of enveloped virus entry into animal cells

“…This interaction appears to HA trimer [38,60]. Current data suggest that a be mediated through a conserved tyrosine in the minimum of three HA trimers is required to form a cytoplasmic domain of E2 and a hydrophobic pocket functional fusion complex [49] and that the trans-on the capsid protein [188,189]. Chemical crossmembrane domain of HA is crucial for fusion.…”

Intrinsically disordered proteins of viruses: Involvement in the mechanism of cell regulation and pathogenesis

“…SFV belongs to the Alphavirus genus that has enveloped positive-strand RNA with an icosahedral nucleocapsid and spherical morphology. 335,336 The N-terminal region of SFV polyprotein (residues 1-267) is an intramolecular serine protease that cleaves itself off after the Trp267 from the rest of the polyprotein segment and provides a mature capsid protein. After this auto cleavage process, the free carboxyl group of Trp267 interacts with catalytic triad consisting of amino acid His145, Asp167, and Ser219 and leads to inactivation of the enzyme.…”