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 a ll other restriction enzymes with known structures, MspI recognizes the pal indromic tetranucleotide sequence 5'-C/CGG and cleaves it as indicated by t he '/' to produce DNA products with 5' two-base overhangs. Owing to the nat ure of its cleavage pattern, it is likely that MspI would represent a new s tructural class of restriction endonucleases. Crystals of the dimeric MspI restriction enzyme bound to a duplex DNA molecule containing the specific r ecognition 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 Angstrom, beta = 109.7 degrees. The crystals contain one dimeri c complex in the asymmetric unit. A complete native data set has been colle cted to a resolution of 2.05 Angstrom by cryo-crystallographic methods, wit h an R-merge of 4.0%.