from Wade C. Winkler writing in Bacillus: Cellular and Molecular Biology (Second edition):
Bacterial genetic regulation is generally assumed to occur at the level of transcription initiation through the use of transcription factors. Regulatory mechanisms that take place post-transcription initiation are sometimes treated as anomalies - as exceptions to the rule. However, the actual degree of usage for post-initiation regulatory strategies in bacteria still remains to be fully determined. As evidence to this fact, recent research has significantly expanded the general understanding of post-initiation regulation in Bacillus subtilis and other bacteria. Regulatory RNAs are now predicted to control expression of numerous fundamental biochemical pathways that together constitute greater than 4% of the B. subtilis genome. Therefore, post-initiation regulation is a vital layer of bacterial genetic circuitry that still remains to be fully revealed.
Further reading: Bacillus: Cellular and Molecular Biology (Second edition)