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 ru bella virus and its wild progenitor virus (TO-336wt) have been determined a nd compared with each other. There were 21 differences in the nucleotide se quences between the TO-336vac and the TO-336wt: 13 in the nonstructural pro tein open reading frame (NSP-ORF), five in the structural protein open read ing frame (SP-ORF) and three in the untranslated regions (UTRs) (one in eac h 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 t he SP-ORF. Of the eight substitutions in NSP-ORF, four (amino acids (aa) 32 0, 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 w ithin the helicase motif. Both of the two residues (aa 890 and 954) in the SP-ORF were within the El gene. The predicted second structure of the 5'UTR of the TO-336vac was identical to that of TO-336wt. Comparing the TO-336 s equences with other four strains, Therien and M33 (wild viruses), and RA27/ 3 and Cendehill (vaccine viruses), the mutations responsible for attenuatio n 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. (C) 2001 Elsevier Science Ltd. All rights reserved.