Restriction Endonucleases that Bridge and Excise Two Recognition Sites from DNA

• Published in: Journal of molecular biology Vol. 367; no. 2; pp. 419 - 431
• Main Authors: Marshall, Jacqueline J.T., Gowers, Darren M., Halford, Stephen E.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 23-03-2007; Elsevier
• Subjects: Binding Sites; Deoxyribonucleases, Type II Site-Specific - chemistry; DNA - chemistry; DNA Cleavage; DNA excision; DNA looping; DNA–protein interaction; enzyme mechanism; Nucleic Acid Conformation; Plasmids; restriction enzyme; Substrate Specificity; SC; R-M; OC; DNA looping; U; DNA excision; FLL; restriction enzyme; enzyme mechanism; KOAc, Mg(OAc)2 and Tris-OAc; AdoMet; DNA–protein interaction
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2006.12.070

Most restriction endonucleases bridge two target sites before cleaving DNA: examples include all of the translocating Type I and Type III systems, and many Type II nucleases acting at their sites. A subset of Type II enzymes, the IIB systems, recognise bipartite sequences, like Type I sites, but cut specified phosphodiester bonds near their sites, like Type IIS enzymes. However, they make two double-strand breaks, one either side of the site, to release the recognition sequence on a short DNA fragment; 34 bp long in the case of the archetype, BcgI. It has been suggested that BcgI needs to interact with two recognition sites to cleave DNA but whether this is a general requirement for Type IIB enzymes had yet to be established. Ten Type IIB nucleases were tested against DNA substrates with one or two copies of the requisite sequences. With one exception, they all bridged two sites before cutting the DNA, usually in concerted reactions at both sites. The sites were ideally positioned in cis rather than in trans and were bridged through 3-D space, like Type II enzymes, rather than along the 1-D contour of the DNA, as seen with Type I enzymes. The standard mode of action for the restriction enzymes that excise their recognition sites from DNA thus involves concurrent action at two DNA sites.