Which of the following post-transcriptional mRNA modifications provide protection after export?

• A. 5' cap only
• B. 3' poly-A tail only
• C. 5' guanine cap and 3' poly-A tail
• D. No modifications

Answer: (C)

The protections come from having both the 5' cap and the 3' poly-A tail. The 5' cap (a 7-methylguanosine) shields the 5' end from degradation and helps recruit translation initiation factors, which is vital as the mRNA becomes active in the cytoplasm. The 3' poly-A tail protects the mRNA’s 3' end from exonucleases and, with poly(A)-binding proteins, promotes stability and efficient translation by helping form a loop that enhances ribosome recycling. Together, these modifications maximize mRNA stability after export and support productive translation, so having both is the most protective option. An mRNA with only the cap or only the tail would still be vulnerable to degradation at the other end, and no modifications would offer little protection.