Restriction endonucleases play a very important role in genetic engineering and 
DNA mapping. Among hundreds of restriction endonucleases, the Eco R1 enzyme is 
the most useful and widely investigated enzyme. After sonication and 
ultracentrifugation, crude extracts of E. coli RY 13 were purified by employing 
the polyethyleneimine precipitate, ammonium sulfate precipitate and heparin 
Sepharose-4B affinity column chromatography. The Eco R1 enzyme were purified at 
about 42 folds and the specific activity was about 100,000 U/mg of protein. The 
whole purification procedure was finished within two days. The recovery was 
about 42%. The enzyme was sufficiently concentrated for direct specific DNA 
hydrolysis.