DNA RECOGNITION AND CLEAVAGE BY THE LAGLIDADG HOMING ENDONUCLEASE I-CREI

The structure of the LAGLIDADG intron-encoded homing endonuclease I-Cr el bound to homing site DNA has been determined. The interface is form ed by an extended, concave beta sheet from each enzyme monomer that co ntacts each DNA half-site, resulting in direct side-chain contacts to 18 of the 24 base pairs across the full-length homing site. The struct ure indicates that I-Crel is optimized to its role in genetic transpos ition by exhibiting long site-recognition while being able to cleave m any closely related target sequences. DNA cleavage is mediated by a co mpact pair of active sites in the I-Crel homodimer, each of which cont ains a separate bound divalent cation.