Complex transcriptional control of the antibiotic regulator afsS in XXXX : PhoP and AfsR are overlapping, competitive activators.

@entity25068 @entity7726 @entity1391 @entity377
The afsS gene of several @entity25068 species encodes a small sigma factor-like protein that acts as an activator of several pathway-specific regulatory genes (e.g., actII-ORF4 and redD in @entity25068 ). The two pleiotropic regulators AfsR and PhoP bind to overlapping sequences in the -35 region of the afsS promoter and control its expression. Using mutated afsS promoters containing specific point mutations in the AfsR and PhoP binding sequences, we proved that the overlapping recognition sequences for AfsR and PhoP are displaced by 1 @entity377 . Different @entity377 positions are important for binding of AfsR or PhoP, as shown by electrophoretic mobility shift assays and by reporter studies using the luxAB gene coupled to the different promoters. Mutant promoter M5 (with a @entity377 change at position 5 of the consensus box) binds AfsR but not PhoP with high affinity (named "superAfsR"). Expression of the afsS gene from this promoter led to overproduction of actinorhodin. Mutant promoter M16 binds PhoP with extremely high affinity ("superPhoP"). Studies with /\afsR and /\phoP mutants (lacking AfsR and PhoP, respectively) showed that both global regulators are competitive transcriptional activators of afsS. AfsR has greater influence on expression of afsS than PhoP, as shown by reverse transcriptase PCR (RT-PCR) and promoter reporter (luciferase) studies. These two high-level regulators appear to integrate different nutritional signals (particularly @entity1391 limitation sensed by PhoR), @entity7726 , and other still unknown environmental signals (leading to AfsR phosphorylation) for the AfsS-mediated control of biosynthesis of secondary metabolites.
