Spontaneous RT mutants and mutations.

The 30 mutants were recovered from 7517 screened plaques and include two isolates (RT27 and RT33) in which the primary mutation had no RT− phenotype, although their secondary mutation (or the combination of both) did. None of the other 17 candidates in the series RT1-RT47 displayed primary mutation, but two isolates, RT24 and RT35, had one secondary mutation each (C→U at position 18 and U→C at position 294, respectively). Altogether, 148 mutants were sequenced: [28 RT mutants carrying primary detectable mutations]+[4 next-generation isolates per each of these]+[2 next-generation isolates per each of four RT mutants (RT24, RT27, RT33 and RT35) that lacked detectable primary mutations]. The mutants were obtained in four different screens yielding 8, 5, 6 and 11 mutants in the order shown. Mutations in parentheses are secondary mutations. Mutant positions refer to the target sequence (1 through 591 including the UAG stop codon) that corresponds to Qß genomic positions 1743 through 2333.