Bacterial RNA thermometers – Molecular zippers or switches?
Abstract
The expression of many bacterial mRNAs is controlled by the formation of complex structures in their 5'-untranslated region (5'-UTR). Riboswitches and RNA thermometers are such built-in sensory elements that control the fate of mRNAs in response to environmental conditions. Both are comprised of complex RNA structures that undergo a conformational change when a certain chemical or physical signal is present. Typical RNA thermometers control translation initiation of heat shock or virulence genes by forming a secondary structure that traps the ribosome binding site (RBS). An increase in temperature to 37°C (virulence genes) or higher (heat shock genes) destabilizes the structure, liberates the RBS and permits formation of the translation initiation complex. Fundamental differences between riboswitches and RNA thermometers will be discussed. Furthermore, the presentation will address the following questions: (i) What are the requirements for a functional RNA thermometer? A comparative analysis of various RNA thermometer classes provides some clues. (ii) What are the molecular details of RNA melting? NMR spectroscopy provided insights at base-pair resolution. (iii) Is reversibility of the melting process physiologically relevant? A novel cyanobacterial RNA thermometer and its role in shuting-off heat shock protein synthesis will be presented. (iv) Do all RNA thermometers act by a zipper-like mechanism?
References
Narberhaus, F. 2010. Translational control of bacterial heat shock and virulence genes by temperature-sensing RNAs. RNA biol. 7:84-89. Rinnenthal, J., Klinkert, B., Narberhaus, F. and H. Schwalbe. 2010. Direct observation of the temperature-induced melting process of the Salmonella fourU RNA thermometer at base-pair resolution. Nucleic Acids Res., 38:3834-3847 Kortmann, J., Sczodrok, S., Rinnenthal, J., Schwalbe, H. and F. Narberhaus. 2011. Translation on demand by a simple RNA-based thermosensor. Nucleic Acids Res., in press
