mRNA-mediated detection of environmental conditions.

Bacteria inhabit an amazing variety of ecological niches and readily adapt to changing environmental conditions. Precise monitoring of external and internal parameters is a prerequisite for the induction of appropriate stress responses. Proteins are often used as sensing devices. However, there is now accumulating evidence that the 5' end of mRNA can be responsive to environmental stimuli. The folding of certain mRNA species is thermally controlled. RNA-based thermosensors modulate the efficiency of translation by controlling the accessibility of translation initiation signals that are captured in hairpin structures under repressing conditions. Recently, it has been recognized that mRNA can also sense physiological signals other than temperature. The overall structure of several vitamin-regulated leader mRNAs depends on the availability of the respective effector molecule. Binding of the vitamin or its precursor to the transcript impairs ribosome binding. Most likely, detection of environmental conditions by sensory RNAs is an emerging concept that is likely to extend much beyond the presently known examples.