Question

Restriction Endonuclease type I is involved in:

• A. Endonuclease and Methylase
• B. Cleaving and Methylation
• C. Cut DNA within palindromic sequences
• D. Cut DNA within non-palindromic sequences

Hint:

Type II restriction enzymes are very precise, cut at or near the recognition site, and are useful for various applications in molecular biology, while type I enzymes cleave DNA at random sites and are not suitable for targeted applications.

Answer 1

The Correct Option is A

Type I restriction enzymes possess both DNA-cleaving (endonuclease) and DNA-modifying (methyl-transferase) functions. They:
• Identify specific DNA sequences but sever DNA at random locations distant from the recognition site.
• Methylate specific bases within the recognition sequence, thereby safeguarding the host DNA from cleavage.
This dual functionality is a defining characteristic of Type I restriction enzymes, distinguishing them from other types that primarily perform cleavage. For example, Type II enzymes cleave DNA at precise sites, whereas Type III enzymes cleave DNA at a specific sequence, though not at the recognition site itself.