Comparative studies of A/Leningrad/134/57 wild-type and 47-times passaged cold-adapted mutant influenza viruses: oligonucleotide mapping and RNA-RNA hybridization studies.

Direct biochemical evidence for the existence of mutations in five of the RNA segments of the A/Leningrad/134/57 cold-adapted 47th passage mutant as compared with its wild-type progenitor has been obtained using two techniques. T1 oligonucleotide mapping of total viral RNA as well as of individual RNA segments revealed changes in RNAs 4, 5 and 6. Analysis of S1 nuclease-treated RNA-RNA hybrids on polyacrylamide gels revealed changes in at least one of the polymerase genes as well as in RNAs 4, 5, 6 and 7. These findings provide a direct demonstration for the existence of multiple mutations in the cold-adapted mutant vaccine strain.