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. 2010 Mar 26;6(3):e1000723. doi: 10.1371/journal.pcbi.1000723

Figure 2. Type 1 fimbriae genetic regulatory network—the fim switch circuit.

Figure 2

Structural fimbriae subunits are encoded by fimA and other downstream genes, which are transcribed when the fim switch is in the ON position (as shown here – also see Figure 1). Recombinases Inline graphic and Inline graphic bind to Inline graphic/Inline graphic and invert the switch with different rates (Inline graphic is strongly biased in the ON-to-OFF direction, while Inline graphic is close to fair). A small protein, Inline graphic, acts in a temperature-dependent manner and represses the expression of the two recombinases. Inline graphic stimulates and inhibits switching based on its occupancy of three Inline graphic sites, while its expression is also repressed by Inline graphic. Inline graphic is required for any observable phase variation as it plays a structural role during switching through its ability to produce sharp bends in the DNA.