THE CARBOXY-TERMINAL DOMAIN OF SENDAI VIRUS NUCLEOCAPSID PROTEIN IS INVOLVED IN COMPLEX-FORMATION BETWEEN PHOSPHOPROTEIN AND NUCLEOCAPSID-LIKE PARTICLES

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 pr oteins form a polymerase complex and are associated with the nucleocap sid core (NP/RNA complex). The NP protein has recently been shown to b e composed of two domains. While the amino-terminal domain I encapsida tes RNA and gives rise to the characteristic helical nucleocapsid stru cture, the precise function of the carboxy-terminal domain II remained unclear. It was however supposed to be involved in binding the polyme rase complex. To test this hypothesis, we established a cosedimentatio n assay which detects complex formation between P protein and nucleoca psid-like (NC-like) particles. Four mutant NC-like particles all carry ing amino acid deletions in domain II of the NP protein were tested. C omplex formation was abolished after deletion of amino acids 426-497 o r 456-524, while deletions of amino acids 400-415 or 414-439 had no in fluence on the interaction. The results indicate that domain II of NP protein is involved in binding P protein to nucleocapsids. The functio n and position of a putative P protein binding site in domain II are d iscussed, (C) 1994 Academic Press, Inc.