Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 244

Some enveloped RNA-containing viruses, such as Semliki Forest virus, contain nucleocapsids that are disassembled in the cytoplasm by pH-independent mechanisms. The icosahedral nucleocapsid of this virus is built from a single viral protein, the C protein, which encloses the (+) strand viral RNA. This structure is surrounded by an envelope containing viral glycoproteins E1 and E2, which are arranged as heterodimers clustered into groups of three, each cluster forming a spike on the virus particle surface.

Fusion of the viral and endosomal membranes exposes the nucleocapsid to the cytoplasm (Fig. 5.20). To begin translation of (+) strand viral RNA, the nucleocapsid must be disassembled, a process mediated by an abundant cellular component, the ribosome. Each ribosome binds three to six molecules of C protein, disrupting the nucleocapsid. This process occurs while the nucleocapsid is attached to the cytoplasmic side of the endosomal membrane and ultimately results in disassembly. The uncoated viral RNA remains associated with cellular membranes, where translation and replication begin.