ABSTRACT: The nucleocapsid (N) protein of SARS coronavirus (SARS-CoV) is reported to function in
encapsidating the viral genomic RNA into helical nucleocapsid, and its self-association is believed to be
vital in coating the viral genomic RNA. Characterization of SARS-CoV N multimerization may thereby
help us better understand the coronavirus assembly. In the current work, using the yeast two-hybrid
technique, an unexpected interaction between residues 1-210 and 211-290 (central region) of the SARSCoV
N protein was detected, and SPR results further revealed that the SR-rich motif (amino acids 183-
197) of SARS-CoV N protein is responsible for such an interaction. Chemical cross-linking and gelfiltration
analyses indicated that the residues 283-422 of the SARS-CoV N protein have multimeric
ability, although the full-length N protein is prone to exist predominantly as dimers. In addition, the
multimeric ability of the C-terminal domain of SARS-CoV N protein could be weakened by the SR-rich
motif interaction with the central region (amino acids 211-290). All of these data suggested that the
SR-rich motif of the SARS-CoV N protein might play an import role in the transformation of the SARSCoV
N protein between the dimer and multimer during its binding to its central region for self-association
or dissociation. This current paper will hopefully provide some new ideas in studying SARS-CoV N
multimerization.