89. Defect in poly-A tail formation in eukaryotic mRNA leads to
(A) Increased translation of the resulting mRNA
(B) Decreased translation of the resulting mRNA
(C) Premature transcription termination
(D) Decreased mRNA stability
Defect in poly-A tail formation reduces mRNA stability and translation efficiency in eukaryotic cells. The correct answer to the query is (D) Decreased mRNA stability.
Correct Answer
A defect in poly-A tail formation leads to (D) Decreased mRNA stability. The poly-A tail, added post-transcriptionally by poly-A polymerase, protects mRNA from 3′ exonucleases and enhances stability. Without proper polyadenylation, mRNA degrades rapidly, reducing its lifespan.
Option Analysis
(A) Increased Translation
Incorrect. Poly-A tails bind PABP, which interacts with eIF4G to form a closed-loop mRNA structure promoting translation initiation. Defective tails shorten or absent, reducing PABP binding and translation efficiency.
(B) Decreased Translation
Partially related but incorrect primary effect. Short poly-A tails lower translation by disrupting cap-PABP synergy, but the dominant outcome is instability-driven decay before translation impacts fully manifest.
(C) Premature Transcription Termination
Incorrect. Polyadenylation signals (AAUAAA) trigger cleavage and poly-A addition after transcription elongation. Defects affect 3′ processing, not polymerase II termination directly.
(D) Decreased mRNA Stability
Correct. Poly-A tails prevent deadenylation-triggered decapping and degradation. Defects expose mRNA to exonucleases, causing rapid turnover.
