Monitoring Equilibrium Changes in RNA Structure by 'Peroxidative' and 'Oxidative' Hydroxyl Radical Footprinting
Summary
This protocol describes how to quantify the Mg(II)-dependent formation of RNA tertiary structure by two methods of hydroxyl radical footprinting.
Abstract
RNA molecules play an essential role in biology. In addition to transmitting genetic information, RNA can fold into unique tertiary structures fulfilling a specific biologic role as regulator, binder or catalyst. Information about tertiary contact formation is essential to understand the function of RNA molecules. Hydroxyl radicals (•OH) are unique probes of the structure of nucleic acids due to their high reactivity and small size.1 When used as a footprinting probe, hydroxyl radicals map the solvent accessible surface of the phosphodiester backbone of DNA1 and RNA2 with as fine as single nucleotide resolution. Hydroxyl radical footprinting can be used to identify the nucleotides within an intermolecular contact surface, e.g. in DNA-protein1 and RNA-protein complexes. Equilibrium3 and kinetic4 transitions can be determined by conducting hydroxyl radical footprinting as a function of a solution variable or time, respectively. A key feature of footprinting is that limited exposure to the probe (e.g., ‘single-hit kinetics’) results in the uniform sampling of each nucleotide of the polymer.5
In this video article, we use the P4-P6 domain of the Tetrahymena ribozyme to illustrate RNA sample preparation and the determination of a Mg(II)-mediated folding isotherms. We describe the use of the well known hydroxyl radical footprinting protocol that requires H2O2 (we call this the ‘peroxidative’ protocol) and a valuable, but not widely known, alternative that uses naturally dissolved O2 (we call this the ‘oxidative’ protocol). An overview of the data reduction, transformation and analysis procedures is presented.
Protocol
Discussion
Hydroxyl radical footprinting is a valuable tool to assess the solvent accessible surface area of nucleic acids. Qualitative and quantitative formation of tertiary structure14 can be followed as a function of parameters such as ion type and concentration, pH, temperature, binding proteins or folding co-factors. The compelling combination of a straight forward and inexpensive protocol and the resulting solvent accessibility and folding information on a single-nucleotide level makes this method very attractive. …
Declarações
The authors have nothing to disclose.
Acknowledgements
This work was supported by grants from the National Institute of Health RO1-GM085130 and National Science Foundation MCB0929394. We thank Dr. Marion Schmidt for her hospitality and for allowing us to film in her laboratory.
Materials
| Name | Company | Cat# |
|---|---|---|
| Sodium Cacodylate (Caution! Toxic) | Sigma | C4945-25g |
| EDTA (0.5 M) | Ambion | AM9260G |
| DEPC treated water | Ambion | AM9915G |
| Sodium Acetate (3 M) | Ambion | AM9740 |
| MgCl2 (1 M) | Ambion | AM9530G |
| Urea | Ambion | AM9902 |
| Sodium Citrate | Sigma | W302600 |
| tRNA | Sigma | R-7876 |
| Sodium-L-ascorbate | Sigma | A7631-25g |
| Fe(NH4)2(SO4)2 . 6 H2O | Sigma | F1543-500g |
| RNase T1 | Fermentas | EN0541 |
| Hydrogen Peroxide (30%) | Sigma | 349887 |
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