ENGINEERING NOVEL RESTRICTION ENDONUCLEASES - PRINCIPLES AND APPLICATIONS

Restriction endonucleases cleave DNA with remarkable sequence specific ity. In this review, we summarize the status of, and prospects for, en gineering restriction endonucleases with new specificities. Such varia nts could be of considerable commercial value because restriction enzy mes are among the most frequently used enzymes in molecular biology, a nd not all the desirable specificities are available. While it has not yet been possible to effect specificity changes, mutants have been de scribed that (1) exhibit relaxed specificity, (2) favour modified subs trates over their natural substrates, (3) discriminate between cleavag e sites located in different sequences, (4) prefer metal ions other th an Mg2+ as cofactors for cleavage, or (5) possess site-specific DNA-ni cking activity.