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Molecular basis for temperature sensing by an RNA thermometer.
Saheli Chowdhury1, Christophe Maris, Frédéric H-T Allain
1Institute of Molecular Biology and Biophysics, ETH Zurich, Zürich, Switzerland.
The EMBO Journal
|May 20, 2006
Summary
Bacterial RNA thermometers sense temperature changes via 3D structural shifts. This study reveals how RNA thermometers regulate translation by releasing the ribosome binding site during heat shock, without needing accessory factors.
Area of Science:
- Molecular Biology
- Structural Biology
- Biophysics
Background:
- Regulatory RNA elements, such as riboswitches, undergo conformational changes in response to cellular signals.
- RNA thermometers are a class of regulatory RNA elements that sense temperature fluctuations to control gene expression.
- These elements are crucial for bacterial adaptation to environmental changes, particularly during stress responses like heat shock.
Purpose of the Study:
- To determine the first 3D Nuclear Magnetic Resonance (NMR) structure of the functional domain of a conserved bacterial RNA thermometer.
- To elucidate the molecular mechanism by which RNA thermometers sense temperature and regulate translation.
- To investigate the role of specific RNA structural features in thermosensing.
Main Methods:
- Three-dimensional (3D) Nuclear Magnetic Resonance (NMR) spectroscopy was used to determine the structure of the RNA thermometer.
- Structural analysis focused on the region containing the ribosome binding site and its accessibility at different temperatures.
- Genetic manipulation, including deletion of key residues, was employed to assess the impact on thermosensing ability.
Main Results:
- The 3D NMR structure revealed a conserved bacterial RNA thermometer with an occluded ribosome binding site at normal temperatures (30°C).
- A region with weak hydrogen bonds adjacent to the Shine-Dalgarno sequence was identified as critical for heat-induced destabilization.
- At elevated temperatures (42°C), structural destabilization releases the ribosome binding site and start codon, enabling translation initiation.
- Deletion of a conserved guanine residue abolished thermosensing, resulting in a stable RNA helix.
Conclusions:
- Bacterial RNA thermometers can sense temperature changes intrinsically through structural rearrangements.
- The identified weak hydrogen bond network is crucial for the thermosensing mechanism.
- RNA thermometers do not require accessory factors to detect temperature shifts and regulate translation.