Restriction Enzyme Classes—ATP Requirement Which class of restriction endonucleases typically does not require ATP hydrolysis for DNA cleavage under standard reaction conditions?

Introduction / Context:
Restriction enzymes are grouped by cofactor requirements and cleavage properties. Understanding these differences is important for planning cloning reactions and selecting appropriate buffers and cofactors.

Given Data / Assumptions:

• Type II enzymes (e.g., EcoRI, BamHI) cleave at or near their recognition sites.
• Type I and Type III enzymes are multi-subunit, often requiring ATP for translocation before cleavage.
• Many Type II enzymes require Mg2+ but not ATP.

Concept / Approach:
Identify the enzyme class used routinely in molecular cloning for precise site-specific cuts without ATP. Type II restriction endonucleases fulfill this role, explaining their dominance in laboratory protocols. By contrast, Type I and III systems are more complex and ATP-dependent for DNA tracking activities prior to cleavage.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer buffer recommendations for Type II enzymes include Mg2+ and salt but no ATP, corroborating the classification.

Why Other Options Are Wrong:

• Type I/III: require ATP for translocation and cleavage.
• Type IV: modification-dependent nucleases with varied requirements; not the standard ATP-independent cutters used in cloning.

Common Pitfalls:
Generalizing properties from one class to all; assuming ATP is universally needed for nucleases.

Final Answer:
Type II