Crystal structure of a group I intron splicing intermediate

Area of Science:

• Molecular Biology
• Structural Biology
• RNA Biology

Background:

• Bacterial group I self-splicing introns are crucial genetic elements involved in RNA processing.
• Understanding their mechanism requires detailed structural information, particularly regarding their complex RNA folds.
• Previous studies lacked a molecular view of the intact intron-exon complex during splicing.

Purpose of the Study:

• To determine the high-resolution crystal structure of an intact bacterial group I self-splicing intron bound to its exons.
• To elucidate the molecular architecture and tertiary interactions governing the intron's complex RNA fold.
• To provide a structural basis for understanding the mechanism of RNA splicing, specifically the exon ligation step.

Main Methods:

• X-ray crystallography was used to obtain the crystal structure of the intron-exon complex.
• Detailed analysis of tertiary hydrogen bonding and base stacking interactions within the RNA fold.
• Hydroxyl radical footprinting was employed to validate the structural model and assess solvent accessibility.

Main Results:

• The crystal structure reveals an intact intron trapped prior to exon ligation, showcasing a complex RNA fold.
• Key structural features include a pseudoknot belt, tetraloop-receptor motifs, a minor groove triplex, and a mu-shaped single-stranded element (J8/7).
• Extensive base stacking interactions (90% of possible) stabilize the intricate RNA architecture, validated by footprinting experiments.

Conclusions:

• The determined structure provides the first molecular view of the pre-exon ligation state of a bacterial group I self-splicing intron.
• The findings reveal critical interactions and architectural principles essential for RNA splicing.
• Proposed models suggest significant tRNA exon motion during the splicing process, offering new mechanistic insights.