Nucleases

thumb|Depiction of the restriction enzyme (endonuclease) [[HindIII cleaving a double-stranded DNA molecule at a valid restriction site ().]]

EcoRI (pronounced "eco R one") is a type II restriction enzyme isolated from Escherichia coli. It cleaves DNA double helices into fragments at specific sites, and is also a part of the restriction modification system. The enzyme's name originates from the species from which it was isolated: "E" denotes generic name (Escherichia), "co" denotes species name (coli), "R" represents the strain (RY13), and the "I" denotes that it was the first enzyme isolated from this strain.

thumb|300px|Eco RII dimer based on [[Protein Data Bank|PDB ID 1NA6 ]] EcoRII (pronounced 'eco R two') is an Restriction endonuclease enzyme (REase) of the restriction modification system (RM) naturally found in Escherichia coli, a Gram-negative bacteria. Its molecular mass is 45.2 kDa, being composed of 402 amino acids.