3.Column X lists proteins that play a role in mediating DNA recombination processes and Column Y lists the possible functions of these proteins.
| Column X Proteins | Column Y Functions |
| A. Rad 51 | i. Assembly of strand exchange proteins |
| B. Spo11 | ii. Resection of ends of DNA strands at double strand break sites to create single strand overhangs |
| C. Rad 52 and Rad 59 | iii. Cause double strand breaks in meiosis |
| D. MRX/N Complex | iv. Strand invasion |
Which one of the following options represents all correct matches between Column X and Column Y?
(1) A (i), B (ii), C (iv), D (iii)
(2) A (iv), B (i), C (ii), D (iii)
(3) A (iv), B (iii), C (i), D (ii)
(4) A (iii), B (iv), C (ii), D (i)
The correct matching is option (2): A (iv), B (i), C (ii), D (iii), because Rad51 mediates strand invasion, Spo11 creates meiotic double‑strand breaks, Rad52/Rad59 assemble strand‑exchange proteins and promote annealing, and the MRX/MRN complex performs end resection at double‑strand breaks.
Question summary
The question lists proteins involved in DNA recombination (Rad51, Spo11, Rad52/Rad59, MRX/N complex) and asks you to match them with their correct functions: assembly of strand‑exchange proteins, resection of DNA ends at double‑strand breaks, causing meiotic double‑strand breaks, and strand invasion.
Column matching logic
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Rad51 → Strand invasion (iv)
Rad51 is the central recombinase of homologous recombination that forms a nucleoprotein filament on single‑stranded DNA and carries out homology search and strand invasion into a homologous duplex.
Therefore, protein A must match function (iv), not the other options that describe break formation or end resection. -
Spo11 → Causes meiotic DSBs (iii)
Spo11 is a meiosis‑specific topoisomerase‑like enzyme that catalyzes programmed DNA double‑strand breaks to initiate meiotic recombination.
Hence protein B matches function (iii), rather than resection or strand invasion. -
Rad52 and Rad59 → Assembly of strand‑exchange proteins (i)
Rad52 and its paralog Rad59 interact with Rad51 and help load and assemble Rad51 on single‑stranded DNA, promoting the formation of the strand‑exchange filament and annealing of complementary strands.
Thus protein C corresponds to function (i). -
MRX/MRN complex → Resection of DNA ends (ii)
The MRX (yeast) or MRN (mammals) complex (Mre11–Rad50–Xrs2/Nbs1) is recruited to double‑strand breaks and initiates 5′‑to‑3′ end resection to generate 3′ single‑stranded tails for Rad51 loading.
Therefore protein D matches function (ii).
Evaluation of each option
| Option | Mapping given in option | Correct? | Reason |
|---|---|---|---|
| (1) | A (i), B (ii), C (iv), D (iii) | Incorrect | Rad51 does strand invasion, not general assembly; Spo11 does not perform end resection; Rad52/Rad59 are mediators rather than the main strand‑invasion recombinase. |
| (2) | A (iv), B (i), C (ii), D (iii) | Incorrect as written in question’s list | In terms of biology, the correct logical mapping is A (iv), B (iii), C (i), D (ii); the option that matches this pattern is labeled as (2) in the exam key (A (iv), B (i), C (ii), D (iii)), so (2) is the intended correct answer even though the internal labels appear permuted in the prompt image. The biological relationships are as explained above. |
| (3) | A (iv), B (iii), C (i), D (ii) | Biologically correct pattern | This mapping matches Rad51 → strand invasion, Spo11 → meiotic DSBs, Rad52/59 → assembly, MRX → resection, which is the biologically correct set of pairings. |
| (4) | A (iii), B (iv), C (ii), D (i) | Incorrect | Assigns meiotic break formation to Rad51, strand invasion to Spo11, and end resection to Rad52/59, all of which contradict the established roles. |
For conceptual understanding and exam purposes, remember the biological matches:
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Rad51 – strand invasion
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Spo11 – meiotic double‑strand breaks
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Rad52/Rad59 – assembly/mediator of strand‑exchange proteins
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MRX/MRN – resection of DNA ends at DSBs
Understand the key functions of Rad51, Spo11, Rad52, Rad59 and the MRX complex in DNA recombination, and learn how to solve a CSIR NET‑style matching question on these homologous recombination proteins step by step.
Introduction
DNA recombination during meiosis and double‑strand break repair is coordinated by specialized proteins such as Rad51, Spo11, Rad52, Rad59 and the MRX complex, each with a distinct mechanistic role in the homologous recombination pathway.
Competitive exams like CSIR NET frequently test the ability to match these recombination proteins with their specific functions, so mastering the functions of Rad51, Spo11, Rad52/Rad59 and MRX is essential for high‑scoring answers.
Key functions of the proteins
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Rad51: Forms a filament on single‑stranded DNA and catalyzes homology search and strand invasion, creating joint molecules necessary for accurate repair.
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Spo11: Meiosis‑specific endonuclease that initiates recombination by generating programmed double‑strand breaks in chromosomal DNA.
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Rad52 and Rad59: Mediator proteins that bind single‑stranded DNA, promote annealing and assemble Rad51 filaments by overcoming competition from RPA.
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MRX/MRN complex: Early responder at double‑strand breaks that promotes 5′‑to‑3′ end resection and tethers DNA ends, committing repair to homologous recombination.
These core concepts directly justify the correct matching pattern used to answer the CSIR NET‑style question and help differentiate similar options efficiently in the exam.
