A single active-site region for a group II intron.

Despite the biological importance of self-splicing group II introns, little is known about their structural organization. Synthetic incorporation of site-specific photo-cross-linkers within catalytic domains resulted in functional distance constraints that, when combined with known tertiary interactions, provide a three-dimensional view of the active intron architecture. All functionalities important for both steps of splicing are proximal before the first step, suggestive of a single active-site region for group II intron catalysis.