Type I Restriction Enzymes - These restriction enzymes recognize the recognition site, but cleave the DNA somewhere between 400 base pairs (bp) to 10,000 bp or 10 kbp right or left.

The cleavage site is not specific. These enzymes are made up of three peptides with multiple functions.

These enzymes require Mg++, A TP and S­ adenosyl methionine for cleavage or for enzymatic hydrolysis of DNA.

These enzymes are studied for general interest rather than as useful tools for genetic engineering.