Small angle X-ray scattering reveals a compact intermediate in RNA folding |
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Authors: | Russell R Millett I S Doniach S Herschlag D |
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Affiliation: | Department of Biochemistry, Stanford University, Stanford, California 94305, USA. |
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Abstract: | 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. |
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