Figure 7

Proposed model for the regulation of P styA. (A) When growing on styrene as sole carbon source, the StyS kinase activity leads to levels of StyR-P such that this protein binds only to the high-affinity actvating-site STY2, while IHF binds to the URE region. This "open" conformation would allow the binding of the RNA polymerase (RNAP) to PstyA, promoting transcription. (B) In carbon catabolite repression conditions (growth on styrene plus glucose) the increased StyS kinase activity would lead to higher levels of StyR-P, so that this protein can bind also to the low-affinity repressive-sites STY1 and STY3, displacing IHF from the URE region. This "closed" promoter conformation would impair the binding of the RNAP to the promoter. The balance between open and closed promoter conformations would determine a fine modulation of the promoter activity.