Published online 12 October 2005
Article |
Molecular beacons as probes of RNA unfolding under native conditions
Cell, Molecular and Developmental Biology and Biophysics Program, Johns Hopkins University 3400 N. Charles St., Baltimore, MD 21218-2685, USA 1T.C. Jenkins Department of Biophysics, Johns Hopkins University 3400 N. Charles St., Baltimore, MD 21218-2685, USA
*To whom correspondence should be addressed. Tel: +1 410 516 2015; Fax: +1 410 516 4118; Email: swoodson{at}jhu.edu
Received August 18, 2005. Revised September 14, 2005. Accepted September 14, 2005.
Hybridization of fluorescent molecular beacons provides real-time detection of RNA secondary structure with high specificity. We used molecular beacons to measure folding and unfolding rates of the Tetrahymena group I ribozyme under native conditions. A molecular beacon targeted against 15 nt in the 5' strand of the P3 helix specifically hybridized with misfolded forms of the ribozyme, without invading the native tertiary structure. The beacon associated with the misfolded ribozyme 300 times more slowly than with an unstructured oligonucleotide containing the same target sequence, suggesting that the misfolded ribozyme core remains structured in the absence of Mg2+. The rate of beacon hybridization under native conditions revealed a linear relationship between the free energy of unfolding and Mg2+ concentration. A small fraction of the RNA population unfolded very rapidly, suggesting parallel unfolding in one step or through misfolded intermediates.
Correspondence may also be addressed to Julia F. Hopkins. Tel: +1 410 516 6776; Fax: +1 410 516 4118; Email: jfhopkins{at}jhu.edu
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