FIG 7.

Schematic representation of sci1 gene cluster regulation. (A) The sci1 T6SS gene cluster is represented on top with the location of the main (P_Sci1) and internal (P₄₅₃₂) promoters. Expanded genetic architectures of these promoters are shown below: +1, transcriptional start; −10 and −35 transcriptional elements (blue); Fur binding box (orange); Dam methylation GATC site (green). (B) Model of regulation of the sci1 main and internal promoters by Fur and Dam. In iron-replete conditions (left), a Fur dimer (hexagons) complexed to iron (dots) is bound to the Fur box, preventing methylation of the GATC site and access by RNA polymerase. Expression from the promoter is repressed (off state). In iron-limiting conditions (right), Fur is released from the promoter, allowing GATC methylation by Dam and binding of RNA polymerase. Expression from the promoter is turned on (on state).