Fig. 12.
Model for the regulation of planosporicin production in P. alba. A basal level of pspXW transcription results in the presence of σPspX-PspW at the cell membrane and leaves the system poised for activation. Low-level transcription of the pspABCTUV operon (1), triggered by an unknown signal, possibly nutrient limitation, results in the production of a small amount of planosporicin (2), eliciting the release of σPspX from PspW (3). This leads to high-level expression of the pspXW, pspEF, and pspJYZQR operons (4). The PspR produced then further activates transcription of pspABCTUV (5), leading to high-levels of planosporicin production (6). White-filled arrows represent transcription, translation, and posttranslational modification. Black arrows represent transcriptional activation. Inhibition is indicated by a blocked line.