The group II intron ribonucleoprotein precursor is a large, loosely packed structure

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Group II self-splicing introns are diverse retroelements.
• They are considered ancestors of spliceosomal introns and DNA retrotransposons.
• Intron-encoded proteins guide RNA folding into active ribonucleoprotein (RNP) complexes.

Purpose of the Study:

• To explore structural differences between precursor and spliced Group II intron RNPs.
• To characterize the structure of the precursor form of the Lactococcus lactis group II intron RNP.

Main Methods:

• Trapping the precursor RNP by deleting the catalytic adenosine nucleophile.
• Sedimentation velocity analysis.
• Size-exclusion chromatography.
• Cryo-electron microscopy (cryo-EM).

Main Results:

• The precursor RNP complex was visualized for the first time.
• The precursor RNP exhibits a large, loosely packed structure.
• This contrasts with the compact structure of spliced introns.

Conclusions:

• Group II intron RNPs undergo a dramatic conformational change from precursor to active states.
• This structural transition is crucial for catalytic activity.
• The findings provide new insights into the evolution of introns and retroelements.