A three-dimensional perspective on exon binding by a group II self-splicing intron.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Self-splicing introns are RNA molecules that can remove themselves from a transcript.
• Group II introns are a major class of self-splicing introns, divided into subgroups IIA and IIB.
• Domain V of group II introns plays a crucial role in catalysis and exon binding.

Purpose of the Study:

• To investigate the structural organization of the exon-binding sites in subgroup IIB self-splicing introns.
• To elucidate the three-dimensional architecture of the complex formed between subgroup IIB introns and their bound exons.
• To understand the role of tertiary interactions in the function of subgroup IIB introns.

Main Methods:

• Chemical footprinting to identify sites of interaction.
• Kinetic dissection of reaction mechanisms.
• Comparative sequence analysis to infer structural relationships.
• Hydroxyl radical footprinting to support structural models.

Main Results:

• Tertiary interactions connect the 5' and 3' exon binding sites in subgroup IIB introns.
• This contrasts with the direct covalent linkage observed in subgroup IIA introns.
• A unique three-dimensional architecture is formed, involving intron domain V and exon-binding sites.
• Close contacts between domain V and an intron-exon pairing were identified.

Conclusions:

• The tertiary interactions in subgroup IIB introns create a distinct structural framework.
• This framework underpins the catalytic activity and 5' exon binding function of domain V.
• The findings reveal a novel mode of exon binding and intron-exon complex formation in RNA splicing.