Question

Which of the following is Type II restriction enzyme?

• A. HindII
• B. EcoK
• C. EcoB
• D. HinfIII

Hint:

Type II restriction endonucleases are the workhorses of genetic engineering because they cleave DNA precisely at or within their recognition sequences, unlike Type I and Type III enzymes, which cleave at random distances.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Restriction endonucleases are enzymes that cleave double-stranded DNA at specific nucleotide sequences.
They are classified into different types (Type I, II, III, and IV) based on their subunit composition, cofactor requirements, and whether they cleave DNA at their recognition site or at a distance from it.

Step 2: Detailed Explanation:
Let us analyze the classification of the restriction enzymes listed in the options:
- HindII: This is a classic Type II restriction endonuclease.
Type II restriction enzymes are homodimers that require only magnesium ($\text{Mg}^{2+}$) as a cofactor.
They recognize symmetric (palindromic) DNA sequences and cleave the phosphodiester backbone precisely within or immediately adjacent to their recognition site.
HindII, isolated from Haemophilus influenzae, was the historically first Type II restriction enzyme ever discovered.
- Let us evaluate why other options are incorrect:
- EcoK and EcoB: These are Type I restriction enzymes.
They are complex, multi-subunit proteins that require S-adenosylmethionine (SAM), ATP, and $\text{Mg}^{2+}$ as cofactors, and they cleave DNA randomly at a considerable distance ($>1000\text{ bp}$) from their recognition sites.
- HinfIII: This is a Type III restriction enzyme, which cleaves DNA approximately 20 to 30 base pairs downstream of its recognition site.
Therefore, HindII is the Type II restriction enzyme.

Step 3: Final Answer:
The Type II restriction enzyme among the options is HindII.