Bacterial 5’ untranslated regions of mRNA, termed thermal switches or thermometers, change their structure in response to temperature change. This structural change provides for the regulation of gene expression. One of such thermal switches, called fourU, is present in the Salmonella species. Mutations of fourU were found to abrogate its regulatory properties. We investigated the thermodynamics of the fourU fragment responsible for its structural changes. All-atom molecular dynamics simulations at various temperatures and spectroscopic experiments in solution were performed for the wild-type fourU and its mutants. We found that the U11C and A8C mutations stabilize the fourU structure in comparison to the wild-type fourU, and the double-point G14A/C25U mutant has the most destabilizing effect on the fourU hairpin 2 responsible for temperature sensing. The G14A/C25U mutant is also the easiest to strand-invade by a complementary oligonucleotide as indicated by fluorescence spectroscopy experiments.

mRNA的细菌5'非翻译区（称为热开关或温度计）会响应温度变化而改变其结构。这种结构变化提供了基因表达的调节。沙门氏菌中有一种这样的热开关，称为fourU物种。发现fourU的突变取消了其调控特性。我们研究了负责其结构变化的fourU片段的热力学。对野生型fourU及其突变体在不同温度下进行了全原子分子动力学模拟，并在溶液中进行了光谱实验。我们发现，与野生型fourU相比，U11C和A8C突变稳定了fourU结构，而双点G14A / C25U突变体对负责温度感测的fourU发夹2的稳定性最大。如荧光光谱实验所示，G14A / C25U突变体也是最容易被互补寡核苷酸链入侵的分子。