Figure 2.

Regulation of bacterial stress responses. (A) Principle of RNA thermometers. At low temperatures, the ribosomal binding site (RBS) and the AUG start codon of an mRNA encoding for a stress gene is base paired and not accessible. On heat shock, the structure around the RBS melts allowing for ribosome binding (30S and 50S) and translation. (B) Chaperones and proteases link the cellular folding state to stress gene expression. Under nonstress conditions, expression of stress genes is inhibited through (1) inhibition of transcriptional activators by chaperones or proteases that either sequester the regulators or degrade them or (2) repressor proteins that require chaperone assistance for activity. During environmental stress misfolded proteins accumulate, which titrate chaperones and proteases from their regulatory roles and resulting in the expression of stress genes through (1) release or stabilization of transcriptional activators or (2) inactivation of repressor proteins. Expression of stress genes initiates an inactivation feedback loop restoring nonstress gene expression.