Post-transcriptional control by global regulators of gene expression in bacteria.

Several authentic or potential global regulators have recently been shown to act at the post-transcriptional level. This is the case for Hfq (HF-1), which is involved in the regulation of an increasing number of genes in Escherichia coli, and CsrA (RsmA) responsible for controlling the expression of genes for extracellular enzymes and secondary metabolism in Gram-negative bacteria. The cold-shock proteins of the CspA family are able to destabilise mRNA secondary structures at low temperature and, therefore, also seem to act post-transcriptionally. These findings illustrate a more general aspect of post-transcriptional control which, in the past, was generally restricted to regulators acting at a single target. The expression of several global transcriptional regulators, such as the stationary phase and heat-shock sigma factors and H-NS, have also recently been shown to be themselves under post-transcriptional control. These examples underline the importance of this type of control in bacterial gene regulation.