Despite the uncertainty concerning the structure-catalysis relationship of type II endonucleases, site-directed mutagenesis of the restriction endonuclease HindIII has provided much insight into the key amino acid residues involved.
Substitutions of Asn for Lys at residue 125 and Leu for Asp at residue 108 significantly decreased DNA binding and the catalytic function of Hin dIII.