When comparing the original with the mutant the following changes are inferred in the amino acid sequences.
Here, the changes are - Original: ile to mutant: Met
Original: asn to mutant: ser
Original: stop to mutant: trp
Now compare the codons that will be originally altered by this mutagen.
Actual codon is Ile AUA, while the mutated codon is Met AUG
Actual codon is Asn AAC or AAU, while the mutated codon is Ser AGU or AGC
Actual codon is stop codon UGA or UAG, while the mutated codon is Trp UGG
The mutations that occurred are due to T to C or A to G transitions. In mRNA, it is change of A to G.
Hence, there is change in all the three codons.
By changing the base-pairing specificity of T, the mutagen can work. Here it now base pairs with G. The mutagen can change the base-pairing specificity of A and A now pairs with C.