EcoRI (pronounced "eco R one") is a restriction endonuclease enzyme isolated from species E. coli.

Each subunit contains a loop which sticks out from the globular domain and wraps around the DNA when bound.

The solved crystal structure shows that the subunits of the enzyme homodimer interact with the DNA symmetrically.

[9] EcoRI can exhibit non-site-specific cutting, known as star activity, depending on the conditions present in the reaction.

Conditions that can induce star activity when using EcoRI include low salt concentration, high glycerol concentration, excessive amounts of enzyme present in the reaction, high pH and contamination with certain organic solvents.