Mutations of rubella virus vaccine TO-336 strain occurred in the attenuation process of wild progenitor virus.

The sequences of the genomes in the TO-336 vaccine strain (TO-336vac) of rubella virus and its wild progenitor virus (TO-336wt) have been determined and compared with each other. There were 21 differences in the nucleotide sequences between the TO-336vac and the TO-336wt: 13 in the nonstructural protein open reading frame (NSP-ORF), five in the structural protein open reading frame (SP-ORF) and three in the untranslated regions (UTRs) (one in each three UTRs). These mutations resulted in amino acid substitutions at ten residues. Of the ten substitutions, eight were in NSP-ORF and two were in the SP-ORF. Of the eight substitutions in NSP-ORF, four (amino acids (aa) 320, 501, 573 and 704) were in the regions of unknown function, two (aa 1154 and 1159) were within the protease motif, and two (aa 1351 and 1559) were within the helicase motif. Both of the two residues (aa 890 and 954) in the SP-ORF were within the E1 gene. The predicted second structure of the 5'UTR of the TO-336vac was identical to that of TO-336wt. Comparing the TO-336 sequences with other four strains, Therien and M33 (wild viruses), and RA27/3 and Cendehill (vaccine viruses), the mutations responsible for attenuation are thought to differ with each vaccine strain. This is the first report of sequencing in a pair of live attenuated rubella vaccines and their wild-type parent.