Effector-Mediated Interaction of CbbR I and CbbR II Regulators with Target Sequences in Rhodobacter capsulatus

Abstract

ABSTRACT In Rhodobacter capsulatus , genes encoding enzymes of the Calvin-Benson-Bassham reductive pentose phosphate pathway are located in the cbb I and cbb II operons. Each operon contains a divergently transcribed LysR-type transcriptional activator (CbbR I and CbbR II ) that regulates the expression of its cognate cbb promoter in response to an as yet unidentified effector molecule(s). Both CbbR I and CbbR II were purified, and the ability of a variety of potential effector molecules to induce changes in their DNA binding properties at their target promoters was assessed. The responses of CbbR I and CbbR II to potential effectors were not identical. In gel mobility shift assays, the affinity of both CbbR I and CbbR II for their target promoters was enhanced in the presence of ribulose-1,5-bisphosphate (RuBP), phosphoenolpyruvate, 3-phosphoglycerate, 2-phosphoglycolate. ATP, 2-phosphoglycerate, and KH 2 PO 4 were found to enhance only CbbR I binding, while fructose-1,6-bisphosphate enhanced the binding of only CbbR II . The DNase I footprint of CbbR I was reduced in the presence of RuBP, while reductions in the CbbR II DNase I footprint were induced by fructose-1,6-bisphosphate, 3-phosphoglycerate, and KH 2 PO 4 . The current in vitro results plus recent in vivo studies suggest that CbbR-mediated regulation of cbb transcription is controlled by multiple metabolic signals in R. capsulatus . This control reflects not only intracellular levels of Calvin-Benson-Bassham cycle metabolic intermediates but also the fixed (organic) carbon status and energy charge of the cell.