Further Unraveling the Regulatory Twist by Elucidating Metabolic Coinducer-Mediated CbbR- cbb I Promoter Interactions in Rhodopseudomonas palustris CGA010

Thecbb I region ofRhodopseudomonas palustris (Rp. palustris ) contains thecbbLS genes encoding form I ribulose-1,5-bisphosphate (RuBP) carboxylase oxygenase (RubisCO) along with a divergently transcribed regulator gene,cbbR . Juxtaposed betweencbbR andcbbLS are thecbbRRS genes, encoding an unusual three-protein two-component (CbbRRS) system that modulates the ability of CbbR to influencecbbLS expression. The nature of the metabolic signals thatRp. palustris CbbR perceives to regulatecbbLS transcription is not known. Thus, in this study, the CbbR binding region was first mapped within thecbbLS promoter by the use of gel mobility shift assays and DNase I footprinting. In addition, potential metabolic coinducers (metabolites) were tested for their ability to alter thecbbLS promoter binding properties of CbbR. Gel mobility shift assays and surface plasmon resonance analyses together indicated that biosynthetic intermediates such as RuBP, ATP, fructose 1,6-bisphosphate, and NADPH enhanced DNA binding by CbbR. These coinducers did not yield identical CbbR-dependent DNase I footprints, indicating that the coinducers caused significant changes in DNA structure. Thesein vitro studies suggest that cellular signals such as fluctuating metabolite concentrations are perceived by and transduced to thecbbLS promoter via the master regulator CbbR.