Assembly of rubella virus structural proteins into virus-like particles in transfected cells

We have developed a stably transfected CHO cell line (CHO24S) that expresses the three structural proteins of rubella virus (RV). RV proteins C (capsid), E2, and E1 are secreted from CHO24S cells in the form of RV-like particles (RLPs) which form by budding into the cisterna of the Golgi complex. RLPs resemble RV virions in their size and morphology and have an identical buoyant density when purified on sucrose gradients. Release of RLPs into the medium was found to be dependent upon the E1 cytoplasmic tail since deletion or substitution of this domain with the same region from vesicular stomatitis virus G protein abrogated release of RV proteins from transfected cells. These results indicate that the RV 40S genomic RNA is not required for efficient particle assembly. Therefore, RLPs may serve as a convenient source of RV antigen for use in diagnostic assays and as an alternative to live attenuated vaccine strains.