Evolution of sequence specificity in a restriction endonuclease by a point mutation.

Area of Science:

• Molecular Biology
• Enzymology
• Genetics

Background:

• Restriction endonucleases (REases) are crucial for bacterial defense against foreign DNA, exhibiting high sequence specificity.
• The evolution of REase specificity is attributed to mechanisms like genetic recombination, gene duplication, and transposition.
• An alternative hypothesis suggests REases evolved from non-specific nucleases via point mutations.

Purpose of the Study:

• To investigate the role of point mutations in the evolution of restriction endonuclease specificity.
• To demonstrate the generation of a highly site-specific REase from a promiscuous ancestor through a single mutation.

Main Methods:

• Characterization of a naturally occurring highly-promiscuous restriction endonuclease.
• Introduction of a single point mutation into the enzyme's gene.
• Analysis of the mutant enzyme's DNA binding and cleavage activity to assess sequence specificity.

Main Results:

• A single point mutation was identified that significantly altered the enzyme's specificity.
• The modified restriction endonuclease exhibited exquisite site-specificity, contrasting with the parental enzyme's promiscuity.
• This mutation effectively narrowed the recognition sequence of the restriction enzyme.

Conclusions:

• A single point mutation is sufficient to convert a promiscuous restriction endonuclease into a highly specific enzyme.
• This study provides a direct example supporting the hypothesis that point mutations contribute to the evolution of REase sequence specificity.
• The findings offer insights into enzyme evolution and potential strategies for engineering novel restriction enzymes.