The Peking Union Medical College Molecular Mechanism Of Attenuation Of Rubella Virus Vaccine Strain

The vaccine type rubella virus (HPV77 strain) replicates slower and manifests a delayed appearance of cytopathic effect in Vero76 cells as compared to the wild type virus (M33). The change in cytopathic effect coincides with the delayed appearance of both genomic and subgenomic RNA as will as viral structural proteins in the cells. The delayed appearance of the viral proteins in the cells was also evident when the cells infected with the HPV77 virus were treated with lysosomotropic agent such as chloroquine. Binding studies using [³⁵S]-methionine labeled virus showed that the HPV77 virus bound to the cells poorly and the binding was not completely competed out with the cold virus. During the viral infection, host cell DNA directs the synthesis of a cellular factor(s) which is essential for the viral replication. When the synthesis of this cellular factor(s) is terminated at are early stage of viral infection by actinomycin D or by alpha-aminitin, viral replication is impaired.Comparison between the structural proteins of the vaccine strain and the wild strain rubella virus revealed that the E2 protein of the vaccine strain differs in apparent molecular weight by approximately 3 kDa from the wild strain. The difference is not due to the different size of mRNA coding for this protein as determined by Northern blot analysis, but could be due to a deareased glycosylation of the E2 protein of the vaccine strain of rubella - virus as revealed by [³H]-mannose incorporation studies.In order to understand the molecular mechanism of the rubella virusattenuation process, a full length cDNA clone for the 24S subgenomic RNA of the vaccine strain rubella virus has been isolated from a cDNA library made from RNAs of the infected cells. Starting from the first initiator...