Isolation and immunological characterization of the nucleocapsid and membrane proteins of measles virus.

Measles virus nucleoprotein (NP) and matrix (M) components were purified by two different procedures. Antigens were prepared by sedimenting material from 1% Cutscum extracts of infected cells into the interphase between 65 and 40% sucrose and further fractionation of the interphase material in a linear CsCl gradient, density range 1.20 to 1.33 g/ml. NP components contaminated with some M material and cellular actin banded at 1.30 to 1.32 g/ml, but at the low density range of 1.20 to 1.22 g/ml pure M component was demonstrable. Partially denatured antigens were obtained by elution of the 60K NP and 36K M polypeptides after SDS-polyacrylamide slab gel electrophoresis. Rabbit hyperimmune sera were prepared against both purified antigens and isolated polypeptides. All sera reacted only with homologous antigen except the antiserum against NP components isolated from CsCl gradients, which also contained antibodies to the M component. Antibodies against NP antigen stained both intranuclear inclusions and cytoplasmic material in immune fluorescence tests. In contrast, antisera against M antigen only stained the cytoplasm. Since intranuclear nucleocapsids are smooth, whereas intracytoplasmic nucleocapsids are 'fuzzy', this may infer that the fuzziness, at least in part, is caused by M antigen adhering to nucleocapsid components.