Monoclonal antibodies to the P protein of Sendai virus define its structure and role in transcription

Abstract

Four monoclonal antibodies specific for Sendai virus nucleocapsid protein P were used to examine both the antigenic structure of P and its role in transcription. Three distinct antigenic regions were delineated on P by competitive radioimmunoassays (RIAs), and through Western blot analysis all three sites were mapped to a 40,000-MW (40K) Staphylococcus aureus protease V8-digestion fragment, which remains associated with the neucleocapsid structure. To study the function of P, nucleocapsids were treated with saturating amounts of anti-P monoclonal antibodies and it was found that transcription in vitro was inhibited by 60-90%. Data, therefore, are consistent with the conclusion that the P protein is required for transcription and that the 40K protease-resistant core contains the functionally important portion of the molecule. Further analysis of the P structure showed that some of the 40K fragments were linked by disulfide bonds. These results suggest that the protease-resistant 40K fragment is in the carboxyl-terminal half of P, since the three cysteine residues of P are found there (C. Giorgi, B. M. Blumberg, and D. Kolakofsky (1983), Cell 35, 829-836).