Figure 6.

A hypothetical model depicting hrpA-mediated coupling of protein secretion and gene regulation. Arrow 1 indicates that hrpA directly affects the transcription or RNA stability of the hrpRS operon independent of its effects on secretion of Hrp and Avr proteins. Arrow 2 indicates that hrpA indirectly regulates the hrpRS operon through its involvement in secretion of a negative regulator (HrpV?) as well as other Hrp and Avr proteins. The question marks indicate uncertainties in the model regarding whether (i) hrpA affects hrpRS expression directly and/or indirectly through its effects on secretion, (ii) Hrp and Avr proteins are secreted through the pilus, and (iii) a negative regulator (e.g., HrpV) is secreted.