The effect of a nonsense mutation and a nonsense suppressor is shown below using the arc gene from phage P22 as an example. The DNA sequence of the arc gene is shown in blue, the mRNA sequence is shown in black, and the protein sequence is shown in purple. The arc amber mutation is due to a C to T base substitution, resulting in a UAG codon in the mRNA. The changes in the DNA, RNA, and protein sequence are underlined.

(A) Wild-type arc⁺ in a sup⁰ strain:

(B) arc (Am) mutant in a sup⁰ strain:

(C) arc (Am) mutant in a supD strain which has an amber suppressor strain mutation in tRNA^ser:

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Last modified November 29, 2003