FIG. 3.

Correction of substitution mutations in fragment F. (A) Mutations were corrected at nucleotides 19400 and 22051, changing the codons for amino acid 6398 in pp1a/b (amino acid 414 in p59-nsp14) and amino acid 94 in ORF 2a 30-kDa protein. (B) Mutant viruses were engineered with either a Tyr or His at amino acid residue 6398 in the ORF 1b p59-nsp14 paired with either a Leu or Pro at amino acid 94 in the ORF 2a 30-kDa protein. Four viruses were derived, representing the four possible combinations of amino acids at the two sites.