Section 3: Genetics, Cellular and Molecular Biology
CRISPR-Cas9 gene editing
Subtopic: Fundamentals of CRISPR-Cas9 gene editing
Question Statement:
Which of the following enzymes is/are involved in the biogenesis of miRNA?
Options:
(A) Drosha
(B) Cas9
(C) XRCC4
(D) Dicer
Official Answer Key:
A;D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.22)**
**1. Governing Concept**:
- **Topic**: Molecular Biology & microRNA (miRNA) Biogenesis Pathway
- miRNA biogenesis proceeds through sequential processing by RNase III family endoribonucleases:
1. **Drosha**: Nuclear RNase III enzyme that partners with DGCR8 (Pasha) in the microprocessor complex to cleave primary miRNA (pri-miRNA) into a ~70 nt precursor hairpin (pre-miRNA).
2. **Exportin-5**: Translocates pre-miRNA from nucleus to cytoplasm.
3. **Dicer**: Cytoplasmic RNase III enzyme that cleaves the loop of pre-miRNA to generate the mature ~21–25 bp duplex miRNA.
4. **Argonaute (AGO)**: Core catalytic engine of the RNA-induced silencing complex (RISC) that loads the guide strand.
**2. Option Analysis**:
- **Option (A) [Drosha] is CORRECT**: Essential nuclear processor generating pre-miRNA.
- **Option (B) [DNA Polymerase I] is INCORRECT**: Bacterial DNA replication enzyme involved in Okazaki fragment primer removal.
- **Option (C) [Telomerase] is INCORRECT**: Specialized ribonucleoprotein reverse transcriptase elongating telomeric ends.
- **Option (D) [Dicer] is CORRECT**: Cytoplasmic endonuclease generating mature double-stranded miRNA duplexes.
**3. Final Answer**:
- **Correct Options**: **A, D**
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