Restriction endonucleases, which cleave DNA in a site-specific manner, are a fundamental tool of molecular biology. The discovery of endonucleases began in the 1960s and led to commercial availability in the early 1970s. The number of characterized enzymes continues to grow, as does the number of vendors and the size of their product lines. Although many similarities exist among endonucleases in terms of their structures, mechanisms, and uses, important differences remain. Now a staple of molecular biology, restriction endonucleases are an area of active research as models of site-specific DNA recognition, cleavage mechanism, in vivo function, and evolutionary origins. New enzymes continue to be discovered or developed by using protein engineering to modify the specificity of existing enzymes.
