Key result
Trapping the native Lactococcus lactis group II intron RNP complex in its precursor form revealed a large, loosely packed structure that contrasts with compact spliced introns.
The group II intron RNP precursor is a large, loosely packed structure that must undergo a dramatic conformational change to become catalytically active.
Highlights RNP remodeling during group II intron maturation; leaves open functional and evolutionary implications.
Group II self-splicing introns are phylogenetically diverse retroelements that are widely held to be the ancestors of spliceosomal introns and retrotransposons that insert into DNA. Folding of group II intron RNA is often guided by an intron-encoded protein to form a catalytically active ribonucleoprotein (RNP) complex that plays a key role in the activity of the intron. To date, possible structural differences between the intron RNP in its precursor and spliced forms remain unexplored. In this work, we have trapped the native Lactococcus lactis group II intron RNP complex in its precursor form, by deleting the adenosine nucleophile that initiates splicing. Sedimentation velocity, size-exclusion chromatography and cryo-electron microscopy provide the first glimpse of the intron RNP precursor as a large, loosely packed structure. The dimensions contrast with those of compact spliced introns, implying that the RNP undergoes a dramatic conformational change to achieve the catalytically active state.
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Huang et al. (2010) studied this question. Deletion of the adenosine nucleophile vs. Compact spliced introns was evaluated on Structure and dimensions of the intron RNP precursor. Trapping the native Lactococcus lactis group II intron RNP complex in its precursor form revealed a large, loosely packed structure that contrasts with compact spliced introns.
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