Form-determining functions in Sindbis virus nucleocapsids: nucleosomelike organization of the nucleocapsid

Abstract

Purified intact Sindbis virus nucleocapsids were treated at different pH values or with various concentrations of divalent cations, cation chelators, salt, or formamide. The resulting structures were examined by velocity sedimentation, electron microscopy, and protein-protein cross-linking. Changes in each of the test conditions led to alterations in the sedimentation profile of treated nucleocapsids. Appropriate concentrations of formamide or divalent cations generated beaded strandlike structures similar in morphology to those generated from adenovirus cores and nucleosomes. The capsid protein and RNA remained associated with each other at NaCl concentrations s1 M or after treatment of the structures with alkaline pH up to and including pH 10.7. Protein and RNA were dissociated by salt concentrations of >1 M, suggesting that the arginine-rich, amino-terminal portion of the capsid protein is responsible for binding the RNA. Protein-protein cross-linking also indicated that the capsid proteins remained associated in small aggregates under some of the conditions that caused dissociation of the nucleocapsid and suggested the presence of more than one type of protein-protein interaction in the nucleocapsids. Collectively, these data suggest that, like histones and adenovirus core proteins, the Sindbis virus capsid protein serves to package segments of the genome into nucleoprotein beads which are capable of interacting with each other to form the nucleocapsid structure.

Functions of alphavirus nonstructural proteins in RNA replication

“…The capsid protein associates transiently with the 60S subunit of the translating ribosome, and is then transferred to the 42S RNA genome during the assembly of the nucleocapsid (10). The assembly of the nucleocapsid is poorly understood, but RNA-protein interactions probably play an important role (11)(12)(13). E3 plus E2 are translocated as a precursor protein p62, which is co-translationally glycosylated.…”

Sindbis virus as a model for studies of conformational changes in a metastable virus and the role of conformational changes in in vitro antibody neutralisation

“…Alphaviruses are hybrid structures, containing protein and RNA encoded by the viral genome with host derived glycosylation and lipid bilayer [10,11]. While other viruses which contain membranes such as influenza or HIV are polymorphic in structure, the Sindbis virion is a highly symmetrical structure displaying T ¼ 4 icosahedral symmetry of both the glycoprotein shell and the inner nucleocapsid core [12][13][14][15][16]. As a T ¼ 4 structure Sindbis virus contains 240 copies of each structural protein in a 1:1:1 stoichiometric arrangement in two nested protein shells.…”