Figure 3From: Now on display: a gallery of group II intron structures at different stages of catalysisPrecatalytic state and position of the reactants for group II intron splicing. The structure of the precatalytic state in the presence of Ca2+/K+ (4FAQ, [30]) allows the identification of all essential reactive elements. The active site scaffold (green cartoon representation) is composed of highly conserved motifs (J2/3 junction, catalytic triad, two-nucleotide bulge). The intron 5′-end connects to the 5′-exon (blue cartoon representation) via the scissile phosphate (orange sphere) and forms the 5′-splice junction. The base-paired helical structure formed by the intron and the exon binding sites (IBS1, EBS1) determines the fidelity of splicing. Finally, a four-metal heteronuclear center formed by Mg2+ ions (M1-M2, yellow spheres) and K+ ions (K1-K2, violet spheres) promotes catalysis, by correctly orienting and activating the reacting groups, including a water molecule (cyan sphere) that acts as the putative nucleophile in the reaction.Back to article page