Characterization of a Structural Antigen of Rubella Virus Reacting by Gel Precipitation

Two to three gel‐precipitating (GP) antigens of rubella virus were extracted from purified rubella virus by treatment with the nonionic detergents Nonidet P40 and Tween 20. The strongest of these GP antigens was further characterized. This antigen sedimented through a 5–20 per cent sucrose gradient in an ultracentrifuge at an S value of about 3.5. It banded in a CsCl equilibrium gradient at densities of 1.25 to 1.30 g/ml. An identical small‐sized antigen could be extracted from rubella‐infected BHK‐21 cells. This antigen seemed to be part of the rubella virus envelope. Some characteristics of the remaining core particles were determined.