Figure 1.

Three schematic examples for cooperative protein-DNA binding in gene regulation. In panel A, RNAp is recruited by an activating TF, whereby the signal conveyed by the TF is transferred to the transcription level. In panel B, an activator is assisted by a helper protein which does not contact RNAp itself. In panel C, two different TFs bind cooperatively and contact RNAp. These and other motifs are used by cells to implement regulatory functions (30,41), although the actual arrangement of TF binding sites in bacterial genomes is often more complicated, involving a larger number of sites (42).