InterPro: IPR011639 Restriction endonuclease, Eco57I

There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements [1, 2], as summarised below:

• Type I enzymes (EC:3.1.21.3) cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase (EC:2.1.1.72) activities.
• Type II enzymes (EC:3.1.21.4) cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.
• Type III enzymes (EC:3.1.21.5) cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase (EC:2.1.1.72).
• Type IV enzymes target methylated DNA.

This entry represents the restriction endonuclease Eco57I, which recognises asymmetric DNA sequence 5'-CTGAAG and has both restriction (DNA cleavage a short distance away from the recognition site) and modification (methylation) activities residing in a single polypeptide chain [3, 4]. It cleaves 22 bases after C-1. As a methylase, it causes specific methylation on A-5 on one strand, the other strand being methylated by the Eco57IB methylase. Homologues of the Escherichia coli Eco57I restriction endonuclease are found in several phylogenetically diverse bacteria.