Solubility of the EcoRI restriction endonuclease and its purification from an over-producing strain.

The solubility of the EcoRI restriction endonuclease was measured in solutions of varying NaCl concentrations, at different temperatures and in the presence of DNA. The precipitation of the protein was enhanced by low NaCl concentrations, by elevated temperatures, and by the addition of DNA. These observations are discussed in relationship to the interaction of this protein with DNA. The purification of the EcoRI restriction enzyme from a strain of Escherichia coli that over-produces this enzyme was hampered by the insolubility of the protein, and hence the purification procedure was modified to optimize the recovery of active enzyme.