FIG. 5.

Proposed model of regulation of the V. cholerae flagellar transcription hierarchy. The results presented here indicate that FlhG acts as a negative regulator of class I (flrA) transcription, while FlhF acts as positive regulator of class III flagellar promoters, perhaps exerting its function through the modulation of FlrC activity. We have previously shown that FlrB is a positive regulator of class III gene transcription by facilitating the phosphorylation of FlrC (5) and that FlgM is a negative regulator of class IV gene transcription through its function as an anti-σ²⁸ factor (4). flgM is transcribed from a class IV promoter (as shown here) and also from a flagellum-independent promoter (37).