Choose the correct answer from the options given below:

1. (A) – (I), (B) – (II), (C) – (III), (D) – (IV)
2. (A) – (III), (B) – (I), (C) – (IV), (D) – (II)
3. (A) – (I), (B) – (II), (C) – (IV), (D) – (III)
4. (A) – (III), (B) – (IV), (C) – (I), (D) – (II)

   Correct Answer: 2. (A) – (III), (B) – (I), (C) – (IV), (D) – (II)

   These nucleases are essential molecular biology reagents with strict substrate specificities, frequently tested in GATE Life Sciences recombinant DNA technology sections. The matching reflects their unique activities: DNase I nicks DNA, RNase A digests RNA, S1 nuclease targets ss nucleic acids, and RNase H cleaves RNA in hybrids.

   Enzyme Matching & Option Analysis

   A. DNase I → III. Produces single-stranded nicks in DNA

   Endonuclease that hydrolyzes phosphodiester bonds in dsDNA, creating single-strand nicks (not full digestion under standard conditions). Used in footprinting and removing DNA contamination.​

   B. RNase A → I. Cleaves and digests RNA and not DNA

   Pancreatic ribonuclease specific for ssRNA (after C/U residues). Completely digests RNA while sparing DNA; gold standard for RNA removal in DNA preps.​

   C. S1 nuclease → IV. Degrades single-stranded DNA and RNA

   Aspergillus-derived single-strand-specific nuclease. Digests ssDNA/RNA completely; used for mapping, blunt-ending, and probe protection assays.

   D. RNase H → II. Cleaves and digests the RNA strand of RNA-DNA heteroduplex

   Hybrid-specific ribonuclease that degrades RNA strand in RNA:DNA hybrids only (leaves DNA intact). Critical for cDNA synthesis, antisense oligos, and replication.​

   Option Breakdown:

   Option	A→	B→	C→	D→	Correct?
   1	I	II	III	IV	❌ RNase swap
   2	III	I	IV	II	✅ Perfect
   3	I	II	IV	III	❌ C/D reversed
   4	III	IV	I	II	❌ B wrong

   DNA RNA modifying enzymes matching questions test nuclease specificities crucial for recombinant DNA techniques in GATE Life Sciences. This MCQ pairs DNase I (DNA nicking), RNase A (RNA digestion), S1 nuclease (single-strand degradation), and RNase H (hybrid cleavage) with their exact reactions. Master these distinctions for exam success.

   Nuclease Specificity Table

   Enzyme	Substrate Specificity	Key Application ​
   DNase I	dsDNA → nicks	Footprinting, DNA removal
   RNase A	ssRNA (C/U-N)	RNA contamination cleanup
   S1 Nuclease	ssDNA + ssRNA	Blunt ends, mapping
   RNase H	RNA in DNA hybrid	cDNA synthesis

   Mechanism Mnemonics

   • DNase I = Double-strand Nicks

   • RNase A = RNA Annihilator

   • S1 = Single-strand specialist

   • Hybrid RNase = Hybrid-only

   Lab Usage Hierarchy

   text

   DNA cleanup: DNase I
RNA cleanup: RNase A
cDNA polishing: S1 nuclease
RT product: RNase H


   GATE Strategy

   • High Yield: 4-5 Qs in Genetic Engineering (20% weightage)

   • Traps: Confuse S1 (ssDNA/RNA) vs RNase H (hybrid only)

   • PYQ Pattern: Always matching format; remember S1 = universal ss nuclease

   Pro Tip: S1 nuclease digests both ssDNA/RNA, distinguishing it from substrate-specific RNases. RNase H’s hybrid specificity is unique for reverse transcription workflows.​