title: Nucleoside triphosphate-dependent restriction enzymes.
abstract: The known nucleoside triphosphate-dependent restriction enzymes are hetero-oligomeric proteins that behave as molecular machines in response to their target sequences. They translocate DNA in a process dependent on the hydrolysis of a nucleoside triphosphate. For the ATP-dependent type I and type III restriction and modification systems, the collision of translocating complexes triggers hydrolysis of phosphodiester bonds in unmodified DNA to generate double-strand breaks. Type I endonucleases break the DNA at unspecified sequences remote from the target sequence, type III endonucleases at a fixed position close to the target sequence. Type I and type III restriction and modification (R-M) systems are notable for effective post-translational control of their endonuclease activity. For some type I enzymes, this control is mediated by proteolytic degradation of that subunit of the complex which is essential for DNA translocation and breakage. This control, lacking in the well-studied type II R-M systems, provides extraordinarily effective protection of resident DNA should it acquire unmodified target sequences. The only well-documented GTP-dependent restriction enzyme, McrBC, requires methylated target sequences for the initiation of phosphodiester bond cleavage.
authors.affiliation: Department of Chemistry, University of Edinburgh, Joseph Black Building, The King's Buildings, Mayfield Road, Edinburgh EH9 3JJ, UK. david.dryden@ed.ac.uk
authors.forename: D T
authors.initials: DT
authors.lastname: Dryden
authors.forename: N E
authors.initials: NE
authors.lastname: Murray
authors.forename: D N
authors.initials: DN
authors.lastname: Rao
mesh_terms: D004247:DNA / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D015253:Deoxyribonucleases, Type I Site-Specific / Q000378:metabolism*; D015263:Deoxyribonucleases, Type III Site-Specific / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism*
chemical_list: D009711:Nucleotides; D004247:DNA; D015253:Deoxyribonucleases, Type I Site-Specific; D015263:Deoxyribonucleases, Type III Site-Specific