FIG. 7.

Model of the regulation of GX biosynthesis by A-factor and phosphate starvation. Both A-factor and phosphate depletion signals are required for the transcription of griR. GriR binds and activates the griC and griJ promoters, causing the transcription of all of the GX biosynthesis enzymes and production of GX. Because AdpA does not bind the upstream region of griR, AdpA is assumed to activate the griR promoter indirectly. The phosphate depletion signal is also transferred to the griR promoter, although its signaling pathway remains to be elucidated.