STRUCTURAL GENE-PRODUCTS AND MORPHOGENESIS OF A HYBRID BETWEEN RUBELLA-VIRUS AND A HAMSTER LATENT RETROVIRUS

We studied the structural gene products and morphogenesis of the hybri d between rubella virus (RV) and a latent retrovirus (R-type virus or R virus) of a baby hamster kidney cell line, BHK21 /WI-2. In electron microscopic analysis, the rubella virion measures 80 nm in diameter an d has a round nucleoid form with an electron-lucid centre, while R-typ e virus is 110 nm in diameter and has a round nucleoid with radial spo kes. The type 2 hybrid (H2) virion is pleomorphic, ranging from 85 to 1 10 nm in diameter, and has a nucleoid structure similar to R virus, with short spokes. Indirect immunofluorescence staining of H2-infected cells with polyclonal and monoclonal antibodies (mAb) against the RV structural proteins demonstrated expression of the homologous RV gene products. SDS-PAGE of S-35-methionine-labelled proteins in RV- and H2- infected cells revealed that they both produce four major immunoprecip itable proteins, three of which (E2a, E2b and C) are products of the t wo genetic homologous loci (e2 and c). In non-homologous regions, RV-i nfected cells exhibited El protein, while H2-infected cells produced t he Env protein of R virus. Western immunoblotting analysis of RV and H 2 viral proteins with mAb confirmed that H2 virions carry rubella vira l E2 and C proteins and that El protein is carried by RV but not H2 vi rion. These results explained the absence of serological cross-neutral ization of haemagglutination and plaque-forming ability of RV and H2 v iruses.