Crystallization and preliminary X-ray diffraction analysis of MspI restriction endonuclease in complex with its cognate DNA.

The MspI restriction endonuclease is a type II restriction enzyme. Unlike all other restriction enzymes with known structures, MspI recognizes the palindromic tetranucleotide sequence 5'-C/CGG and cleaves it as indicated by the '/' to produce DNA products with 5' two-base overhangs. Owing to the nature of its cleavage pattern, it is likely that MspI would represent a new structural class of restriction endonucleases. Crystals of the dimeric MspI restriction enzyme bound to a duplex DNA molecule containing the specific recognition sequence have been obtained by vapor-diffusion techniques in the presence of polyethylene glycol as precipitant. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 50.2, b = 131.6, c = 59.3 A, beta = 109.7 degrees. The crystals contain one dimeric complex in the asymmetric unit. A complete native data set has been collected to a resolution of 2.05 A by cryo-crystallographic methods, with an R(merge) of 4.0%.