The carboxy-terminal domain of Sendai virus nucleocapsid protein is involved in complex formation between...

The replicative unit of Sendai virus, the nucleocapsid, is composed of the viral genomic RNA and the viral proteins NP, P, and L. P and L proteins form a polymerase complex and are associated with the nucleocapsid core (NP/RNA complex). The NP protein has recently been shown to be composed of two domains. While the amino-terminal domain I encapsidates RNA and gives rise to the characteristic helical nucleocapsid structure, the precise function of the carboxy-terminal domain II remained unclear. It was however supposed to be involved in binding the polymerase complex. To test this hypothesis, we established a cosedimentation assay which detects complex formation between P protein and nucleocapsid-like (NC-like) particles. Four mutant NC-like particles all carrying amino acid deletions in domain II of the NP protein were tested. Complex formation was abolished after deletion of amino acids 426-497 or 456-524, while deletions of amino acids 400-415 or 414-439 had no influence on the interaction. The results indicate that domain II of NP protein is involved in binding P protein to nucleocapsids. The function and position of a putative P protein binding site in domain II are discussed.