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: Understanding the Concept:
RNA interference (RNAi) is a cellular mechanism that silences gene expression. In the laboratory, it is triggered by introducing a small interfering RNA (siRNA) or a short hairpin RNA (shRNA) construct. These constructs must be complementary to a sequence in the target mature messenger RNA (mRNA) to guide the RNA-induced silencing complex (RISC) to cleave and degrade that mRNA.
Step 2: Detailed Explanation:
Let's consider the structure of a gene and its corresponding mature mRNA:
A gene in the DNA contains exons (coding sequences) and introns (intervening, non-coding sequences).
During RNA processing (splicing), the introns are removed from the pre-mRNA, and the exons are joined together to form the mature mRNA.
The mature mRNA consists of a 5' untranslated region (UTR), the coding sequence (derived from exons), and a 3' untranslated region (UTR).
For an RNAi construct to work, it must target a sequence that is actually present in the final mRNA molecule in the cytoplasm.
The 5' UTR, 3' UTR, and exonic regions are all present in the mature mRNA, so they are all valid targets for RNAi.
The intronic region is spliced out and is not present in the mature mRNA. Therefore, an RNAi construct designed against an intron would not find its target in the cytoplasm and would be ineffective at knocking down the gene's expression.
Step 3: Final Answer:
The intronic region is not used for making an RNAi construct because it is not part of the mature mRNA transcript that needs to be targeted for degradation.