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GATE 2025 BT Q.22: solution and answer

GATE 2025 · BTQ.22 · 1 mark · MSQ

Which of the following enzymes is/are involved in the biogenesis of miRNA?

  1. (A)

    Drosha

  2. (B)

    Cas9

  3. (C)

    XRCC4

  4. (D)

    Dicer

See the question in the paper
GATE 2025 BT question 22Tap to open full size

Answer and solution

ANSWER

The enzymes involved in miRNA biogenesis are Drosha and Dicer (Options A and D).

Official answer: A, DSource: Official answer key, GATE 2025 BT (IIT Roorkee)

  1. Recall the miRNA biogenesis pathway: a long primary transcript (pri-miRNA) is processed by two sequential RNase III-family enzymes before it becomes a mature, functional miRNA.

  2. Option A — Drosha: a nuclear RNase III enzyme that, with its partner DGCR8, cleaves pri-miRNA into pre-miRNA (a ~60-70 nt hairpin). This is the first, defining step of miRNA biogenesis. CORRECT.

  3. Option B — Cas9: an RNA-guided DNA endonuclease from the bacterial CRISPR adaptive immune system, used for genome editing. It has no role in endogenous miRNA processing. INCORRECT.

  4. Option C — XRCC4: a scaffold protein that partners with DNA Ligase IV in the non-homologous end joining (NHEJ) pathway of DNA double-strand break repair. It is unrelated to RNA processing. INCORRECT.

  5. Option D — Dicer: a cytoplasmic RNase III enzyme that cleaves the pre-miRNA hairpin (exported from the nucleus via Exportin-5) into the mature miRNA duplex, which is then loaded onto Argonaute to form RISC. CORRECT.

  6. Therefore the enzymes involved in miRNA biogenesis are Drosha (A) and Dicer (D).

KEY IDEA

miRNA biogenesis requires two sequential RNase III-family endonucleases: nuclear Drosha (with DGCR8) converts pri-miRNA to pre-miRNA, and cytoplasmic Dicer converts pre-miRNA to the mature miRNA duplex, which is then loaded into RISC (Argonaute).

WATCH OUT FOR

Confusing Cas9 (a CRISPR genome-editing nuclease with no role in endogenous miRNA processing) or XRCC4 (a DNA double-strand break repair protein) with the RNase III enzymes that actually process miRNA precursors.

From the GATE 2025 BT paper. Every question of this paper · Download the full paper · All 21 Gene expression questions, with notes

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