Question

Type II Restriction Endonucleases are the most important enzymes used for gene cloning. Type-II Restriction endonucleases include

• A. EcoRI
• B. EcoBI
• C. EcoB
• D. EcoP15

Hint:

Type II restriction enzymes are named using a standard nomenclature: 'Eco' refers to the genus and species (*Escherichia coli*), 'R' refers to the strain (RY13), and 'I' is the Roman numeral representing the order of discovery.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Restriction endonucleases are bacterial enzymes that cleave double-stranded DNA at specific recognition sequences.
They are classified into four major classes (Types I, II, III, and IV) based on their subunit structure, cofactor requirements, and cleavage site location relative to their recognition sequence.

Step 2: Detailed Explanation:
Let us analyze the classification of the restriction enzymes listed in the options:
1. Type I Restriction Enzymes (such as EcoB and EcoBI): These are large, multi-subunit complexes that possess both restriction and methylase activities.
They bind to specific recognition sites but cleave the DNA at random locations far from the recognition site (typically $>1000$ base-pairs away), requiring ATP, S-adenosylmethionine (SAM), and magnesium ions. They are not suitable for cloning.
2. Type II Restriction Enzymes (such as EcoRI): These are simpler, homodimeric enzymes that require only magnesium ions as a cofactor.
They cleave the DNA specifically at or within their short, palindromic recognition sequences (typically 4-8 base pairs).
For example, EcoRI recognizes the palindromic sequence:
\[ 5'-\text{GAATTC}-3' \]
and cleaves it to generate sticky ends with 5'-overhangs.
Because they cleave DNA at highly predictable locations, Type II restriction enzymes are essential tools for gene cloning and recombinant DNA technology.
3. Type III Restriction Enzymes (such as EcoP15): These are multi-subunit complexes that cleave DNA approximately 25-28 base pairs downstream of their recognition site. They require ATP and SAM for cleavage.

Step 3: Final Answer:
The Type-II restriction endonuclease among the options is EcoRI, corresponding to option (A).