CARBON MONOXIDE-INDUCED ACTIVATION OF GENE-EXPRESSION IN RHODOSPIRILLUM-RUBRUM REQUIRES THE PRODUCT OF COOA, A MEMBER OF THE CYCLIC-AMP RECEPTOR PROTEIN FAMILY OF TRANSCRIPTIONAL REGULATORS

Induction of the CO-oxidizing system of the photosynthetic bacterium R hodospirillum rubrum is regulated at the level of gene expression by t he presence of CO, In this paper, we describe the identification of a gene that is required for CO-induced gene expression, An Il-kb deletio n of the region adjacent to the previously characterized cooFSCTJ regi on resulted in a mutant unable to synthesize CO dehydrogenase in respo nse to CO and unable to grow utilizing CO as an energy source. A 2.5 k b region that corresponded to a portion of the deleted region compleme nted this mutant for its CO regulation defect, restoring its ability t o grow utilizing CO as an energy source, When the 2.5-kb region was se quenced, one open reading frame, designated cooA, predicted a product showing similarity to members of the cyclic AMP receptor protein (CRP) family of transcriptional regulators, The product, CooA, is 28% ident ical (51% similar) to CRP and 18% identical (45% similar) to FNR from Escherichia coli, The insertion of a drug resistance cassette into coo A resulted in a mutant that could not grow utilizing CO as an energy s ource, CooA contains a number of cysteine residues substituted at, or adjacent to, positions that correspond to residues that contact cyclic AMP in the crystal structure of CRP, A model based on this observatio n is proposed for the recognition of CO by CooA, Adjacent to cooA are two genes, nadB and nadC, with predicted products similar to proteins in other bacteria that catalyze reactions in the de novo synthesis of NAD, A mutant with the cooA-nadBC region deleted displayed an auxotrop hy for nicotinic acid, while the cooA insertion mutant did not.