Volume 7 Issue 9, September 2000

The known X-ray crystal structure of a bacterial RNA polymerase together with systematic site-specific protein nucleic acid crosslinking analyses have allowed the determination of the path of DNA and RNA through RNA polymerase.

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.