Small angle X-ray scattering reveals a compact intermediate in RNA folding.
We have used small angle X-ray scattering (SAXS) to monitor changes in the overall size and shape of the Tetrahymena ribozyme as it folds. The native ribozyme, formed in the presence of Mg2+, is much more compact and globular than the ensemble of unfolded conformations. Time-resolved measurements show that most of the compaction occurs at least 20-fold faster than the overall folding to the native state, suggesting that a compact intermediate or family of intermediates is formed early and then rearranges in the slow steps that limit the overall folding rate. These results lead to a kinetic folding model in which an initial 'electrostatic collapse' of the RNA is followed by slower rearrangements of elements that are initially mispositioned.
Russell
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Department of Biochemistry, Stanford University, Stanford, California 94305, USA.
Millett
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Doniach
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Herschlag
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D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000494:pharmacology; D018360:Crystallography, X-Ray; D017665:Hydroxyl Radical / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008958:Models, Molecular; D009690:Nucleic Acid Conformation / Q000187:drug effects; D020871:RNA Stability / Q000187:drug effects; D016337:RNA, Catalytic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D055672:Static Electricity; D013768:Tetrahymena / Q000201:enzymology / Q000235:genetics*
D016337:RNA, Catalytic; D017665:Hydroxyl Radical; D012964:Sodium; D008274:Magnesium; D002118:Calcium