Final answer:
mRNA surveillance is the process ensuring that only properly processed and complete mRNAs are translated, while those with mutations are degraded, occurring after polyadenylation and splicing within the nucleus.
Step-by-step explanation:
The process that occurs in the nucleus after polyadenylation and splicing, ensuring that the integrity of the transcript for 'correct' mRNAs is maintained for translation, and that mRNAs containing mutations are eliminated by enhanced mRNA decay, is known as mRNA surveillance. This is a critical post-transcriptional regulation aspect that includes checking the mRNA's quality and its suitability for export and translation. After the addition of a 5' methylguanosine cap and a 3' poly-A tail to the pre-mRNA, which protects it from degradation and aids in its export from the nucleus, mRNA surveillance ensures that only properly processed and complete mRNAs proceed to the cytoplasm for protein synthesis. Any defective mRNAs are identified and degraded, preventing the translation of potentially harmful or nonfunctional proteins.