BglII and MunI: what a difference a base makes

Restriction endonucleases are resilient to alterations in their DNA-binding specificities. Structures of the Bg/II and MunI endonucleases bound to the ir palindromic DNA sites, which differ by only their outer base pairs from the recognition sequences of BamHI and EcoRI, respectively, have recently b een determined. A comparison of these complexes reveals surprising differen ces and similarities in structure, and provides a basis for understanding t he immutability of restriction endonucleases.