[1] They are named 'FourU' due to the four highly conserved uridine nucleotides found directly opposite the Shine-Dalgarno sequence on hairpin II (pictured).

At human body temperature, the thermometer structure opens and to allow transcriptional activator protein ToxT translation, facilitating V. cholerae virulence.

[1] A later study used mutant analysis and calculations of enthalpy and entropy to support a cooperative zipper-type unfolding mechanism of FourU hairpin II in response to temperature increase.

of undiscovered RNA thermometers operating alongside sigma factor modules to regulate other related genes as an additional level of control.

Further speculation suggests the simpler RNA thermometer method of gene regulation may have evolved prior to the more complex sigma factor transcription control.