A crystal structure of a tetrameric restriction enzyme, NgoMIV, bound to two DNA duplexes has been determined. Two subunits contact each duplex in much the same manner as a dimeric restriction enzyme recognizing a single site, but the dimeric units are packed back-to-back, placing the duplexes on opposite sides of the tetramer. Interaction with two recognition sites, presumably via looping, enhances NgoMIV activity.
- Stephen E. Halford
- Darren M. Gowers
- Richard B. Sessions