Figure 6. Models for How the MglA–SspA Complex Positively Controls Virulence Gene Expression in F. tularensis .

(A) Contact between a DNA-bound transcription activator and the RNAP-associated MglA–SspA complex activates transcription from a virulence gene promoter. The arrow indicates the transcription start site.

(B) Contact between promoter DNA and the RNAP-associated MglA–SspA complex activates transcription from a virulence gene promoter. In these models, the virulence gene promoters are depicted as being recognized by RNAP holoenzyme containing σ⁷⁰. The RNAP that co-purifies with MglA-TAP appears to contain σ⁷⁰ in stoichiometric amounts (Figure 1B), suggesting that the promoters of MglA/SspA-dependent genes may be σ⁷⁰-dependent.