What post-transcriptional modification protects eukaryotic pre-mRNA from 5' exonucleolytic degradation and assists in ribosome binding?
Answer and explanation
Correct answer: C. Addition of a 7-methylguanosine cap via a 5'-to-5' triphosphate bridge
- Step 1: During transcription elongation, capping enzymes attach a modified guanine to the 5' end. Step 2. The 7-methylguanosine cap is linked through an unusual 5'-to-5' triphosphate bond, protecting mRNA from 5' nucleases and facilitating translation initiation. Answer: Addition of a 7-methylguanosine cap via a 5'-to-5' triphosphate bridge. Why not the others: Polyadenylation occurs at the 3' end, splicing removes introns, and histone methylation alters chromatin, not mRNA.
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