Nucleic Acids Research Advance Access originally published online on April 16, 2007
Nucleic Acids Research 2007 35(9):2965-2974; doi:10.1093/nar/gkm184
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Nucleic Acids Research, 2007, Vol. 35, No. 9 2965-2974
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Thermodynamics and kinetics for base-pair opening in the P1 duplex of the Tetrahymena group I ribozyme
1Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309-0215, USA and 2Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju, Gyeongnam 660-701, Republic of Korea
*To whom correspondence should be addressed. Tel: +1-303-492-6263; Fax: +1-303-492-5894; Email: Arthur.Pardi{at}colorado.edu
Received January 22, 2007. Revised March 14, 2007. Accepted March 14, 2007.
The thermodynamics and kinetics for base-pair opening of the P1 duplex of the Tetrahymena group I ribozyme were studied by NMR hydrogen exchange experiments. The apparent equilibrium constants for base pair opening were measured for most of the imino protons in the P1 duplex using the base catalysts NH3,
or TRIS. These equilibrium constants were also measured for several modified P1 duplexes, and the C-2·G23 base pair was the most stable base pair in all the duplexes. The conserved U-1·G22 base pair is required for activity of the ribozyme and the data here show that this wobble base pair destabilizes neighboring base pairs on only one side of the wobble. A 2'-OMe modification on the U-3 residue stabilized its own base pair but had little effect on the neighboring base pairs. Three base pairs, U-1·G22, C-2·G23 and A2·U21 showed unusual equilibrium constants for opening and possible implications of the opening thermodynamics of these base pairs on the undocking rates of the P1 helix with catalytic core are discussed.