Crystallization and preliminary diffraction analysis of a group I ribozyme from bacteriophage Twort.

Group I introns are catalytic RNAs that are capable of performing a variety of phosphotransesterification reactions including self-splicing and RNA cleavage. The reactions are efficient, accurate and dependent only on the presence of guanosine-nucleotide substrate and sufficient magnesium ion to stabilize the structure of the RNA. To understand how the group I intron active-site facilitates catalysis, crystals of a 242-nucleotide ribozyme bound to a four-nucleotide product RNA have been produced that diffract to 3.6 A resolution. The space group of these crystals is I2(1)2(1)2(1) and the unit-cell parameters are a = 94.6, b = 141.0, c = 210.9 A. A single heavy-atom derivative has been synthesized by covalent modification of the product RNA with iodine.