Final answer:
The rate-limiting step for the decay of nonsense codon-containing mRNA is deadenylation, the shortening of the mRNA's poly-A tail. Polyadenylation, catalyzed by polyadenylate polymerase, is crucial for mRNA stability and translation efficiency, but does not relate directly to mRNA decay. The correct option is B.
Step-by-step explanation:
The rate-limiting step for the decay of nonsense codon-mRNA is deadenylation. This is the process by which the poly-A tail of an mRNA molecule is gradually shortened, eventually leading to decapping and subsequent degradation of the mRNA. The poly-A tail and the 5' cap are crucial for the stability and translation efficiency of the mRNA.
When a ribosome reaches a nonsense codon, the release factors induce the release of the newly synthesized polypeptide, and after many rounds of translation, the mRNA is degraded.
The enzyme polyadenylate polymerase, which is responsible for polyadenylation, adds multiple adenosine monophosphates to the 3' end of the mRNA, which would not occur if the enzyme were blocked.