Figure 9

Model for light-inducible transcriptional control by PmlR2 and PmSB-LOV. PmlR2 binds to the promoter region of the light-inducible P6650 and prevents transcriptional initiation by RNA polymerase holoenzyme containing σ⁷⁰. Upon illumination, PmSB-LOV becomes active and forms a covalent thiol-adduct with FMN. Activated PmSB-LOV associates with PmlR2, abolishing its DNA-binding activity and allowing RNA polymerase to initiate transcription from P6650. Dark incubation causes the covalent FMN-C4a-cysteinyl-thiol adduct to break, leading to dissociation of PmlR2 and PmSB-LOV and inhibition of P6650 by the binding of PmlR2.