# DBT JRF 2022 — Question 75

Exam: DBT JRF 2022 · Section: B · Topic: Molecular Biology › RNA Interference & RISC Complex · Difficulty: Medium

## Question

Which one among the following is an important constituent of RNA induced silencing complex in plants?

## Options

- **A.** Argonaute
- **B.** LHP1
- **C.** RNaseP
- **D.** RNA dependent RNA polymerase

## Answer

Option A

## Explanation

Argonaute proteins and RISC function: RNA interference (RNAi) pathway: 1. Long dsRNA or pre-miRNA is processed by DICER into short ~21–23 nt duplexes (siRNA or miRNA). 2. One strand (guide strand) is loaded into the RISC (RNA-Induced Silencing Complex). 3. RISC is assembled around an ARGONAUTE (AGO) protein: • AGO carries the guide RNA. • PAZ domain: anchors the 3' end of the guide RNA. • PIWI domain: contains the Slicer endonuclease activity (cleaves the target mRNA at the site complementary to positions 10-11 of the guide strand). 4. RISC scans mRNAs for complementary sequences: • Perfect complement (siRNA-like): mRNA cleavage. • Imperfect complement (miRNA-like): translational repression + mRNA destabilisation. AGO2 in humans has active Slicer activity; AGO1, AGO3, AGO4 lack it. Answer: Argonaute is the core catalytic component of RISC that uses guide miRNA/siRNA to silence target mRNAs.

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