The first isolated restriction endonuclease was:

The correct answer is Option (1) → Hind II

Restriction endonucleases cut DNA at specific recognition sequences. The first one to be isolated was Hind II. It always cuts DNA at a fixed point by recognising a particular sequence of six base pairs.

Option (1) Hind II — Correct. It is the first restriction endonuclease that was isolated and characterised.

Option (2) EcoR I — Incorrect. EcoRI from E. coli RY13 is the enzyme the book uses to explain sticky ends, but it was not the first one isolated.

Option (3) BamH I — Incorrect. BamHI comes from Bacillus amyloliquefaciens. It is a restriction site on pBR322, not the first enzyme isolated.

Option (4) Pvu II — Incorrect. PvuII comes from Proteus vulgaris. It is another restriction site on pBR322, not the first enzyme isolated.

Note: A similar question was also asked in CUET (UG) 2026 on 26-05-2026 (Slot 1), on 21-05-2026 (Slot 1), on 19-05-2026 (Slot 2) and on 14-05-2026 (Slot 1), in CUET (UG) 2023 on 22-06-2023 (Slot 3), on 09-06-2023 (Slot 3) and on 01-06-2023 (Slot 3), and in CUET (UG) 2022 on 20-08-2022 (Slot 1).

NCERT Extract:
Restriction Enzymes – “The first restriction endonuclease–Hind II, whose functioning depended on a specific DNA nucleotide sequence was isolated and characterised five years later. It was found that Hind II always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II.”