Question

Which one of the following regions of the target gene is NOT used for making an RNAi construct to knock down its expression

• A. 5' UTR of the mature transcript
• B. 3' UTR of the mature transcript
• C. Exonic region
• D. Intronic region

Hint:

RNAi targets the messenger, not the original blueprint. The messenger (mRNA) is the "spliced" version of the gene, which only contains exons and UTRs. Introns are left behind in the nucleus.

Answer 1

The Correct Option is D

Step 1: RNAi Overview:
RNA interference (RNAi) is a cellular process that silences gene expression. In the lab, it's initiated by introducing small interfering RNA (siRNA) or short hairpin RNA (shRNA). These molecules must match a sequence in the target mature messenger RNA (mRNA) to direct the RNA-induced silencing complex (RISC) to destroy that mRNA.
Step 2: mRNA Structure and RNAi Targeting:
A gene in DNA has exons (coding regions) and introns (non-coding regions).
During RNA processing (splicing), introns are removed from pre-mRNA, and exons are joined to create mature mRNA.
Mature mRNA includes a 5' untranslated region (UTR), a coding sequence (from exons), and a 3' UTR.
For RNAi to function, it must target a sequence present in the final mRNA in the cytoplasm.
The 5' UTR, 3' UTR, and exonic regions are all in mature mRNA, making them valid RNAi targets.
The intronic region is removed by splicing and isn't present in the mature mRNA. Therefore, an RNAi construct targeting an intron won't find its target in the cytoplasm, rendering it ineffective.
Step 3: Conclusion:
Introns aren't used for RNAi constructs because they aren't part of the mature mRNA transcript, which must be targeted for degradation.