Oligomers of the cytoplasmic domain of the p62/E2 membrane protein of Semliki Forest virus bind to the nucleocapsid in vitro.

We analyzed the interaction between the nucleocapsid and synthetic peptides corresponding to the complete or truncated cytoplasmic protein domain of the Semliki Forest virus p62/E2 glycoprotein. We found that the peptide corresponding to the full-length domain efficiently bound nucleocapsids when coupled to a solid matrix via specific antibodies, whereas the shorter one did not. In solution, a substantial fraction of the full-length peptide associated into oligomers. Binding studies showed that it was mostly these oligomers, rather than the monomeric form of the peptide, which were able to interact with the nucleocapsid. Thus, our findings demonstrate a direct interaction between the spike proteins and the viral nucleocapsid. Furthermore, they suggest that this interaction is directed through formation of complexes containing several p62 or E2 subunits.