BplI, a new BcgI-like restriction endonuclease, which recognizes a symmetric sequence

Area of Science:

• Molecular Biology
• Enzymology
• Genetics

Background:

• Bcg I and Bcg I-like enzymes are restriction endonucleases with unique properties.
• These enzymes cleave double-stranded DNA flanking asymmetric recognition sequences.
• Their bifunctionality and dependence on AdoMet distinguish them from other restriction enzymes.

Purpose of the Study:

• To characterize a new Bcg I-like restriction endonuclease, Bpl I, from Bacillus pumilus.
• To investigate the recognition sequence and cleavage mechanism of Bpl I.
• To determine the enzymatic activities and subunit composition of Bpl I.

Main Methods:

• Purification of Bpl I from Bacillus pumilus.
• DNA cleavage assays to determine recognition sequence and cleavage sites.
• Analysis of enzyme activity in the presence of cofactors like AdoMet and AdoHcy.
• Determination of subunit molecular masses using SDS-PAGE.

Main Results:

• Bpl I recognizes a symmetric interrupted sequence (8/13)GAGN5CTC(13/8), unlike other Bcg I-like enzymes.
• Bpl I exhibits bifunctional activity, possessing both DNA cleavage and methyltransferase capabilities.
• The enzyme consists of two polypeptides (approx. 74 and 37 kDa) in a 1:1 ratio.
• Activity is significantly enhanced by S-adenosylhomocysteine (AdoHcy), leading to complete DNA cleavage.

Conclusions:

• Bpl I represents a novel class of Bcg I-like restriction enzymes due to its symmetric recognition sequence.
• The enzyme's bifunctionality and cofactor dependence provide insights into restriction-modification system diversity.
• AdoHcy is a potent activator of Bpl I, enabling complete DNA cleavage.