The gene (crc) responsible for catabolite repression control in Pseudomonas aeruginosa has been cloned and sequenced. Flanking the crc gene are genes encoding orotate phosphoribosyl transferase (pyrE) and RNase PH (rph). New crc mutants were constructed by disruption of the wild-type crc gene. The crc gene encodes an open reading frame of 259 amino acids with homology to the apurinic/apyrimidinic endonuclease family of DNA repair enzymes. However, crc mutants do not have a DNA repair phenotype, nor can the crc gene complement Escherichia coli DNA repair-deficient strains. The crc gene product was overexpressed in both P. aeruginosa and in E. coli, and the Crc protein was purified from both. The purified Crc proteins show neither apurinic/ apyrimidinic endonuclease nor exonuclease activity. Antibody to the purified Crc protein reacted with proteins of similar size in crude extracts from Pseudomonas putida and Pseudomonas fluorescens, suggesting a common mechanism of catabolite repression in these three species.The genus Pseudomonas is noteworthy for its diversity in habitat and physiology. Some Pseudomonas strains are able to use over 100 organic compounds as the sole or principal source of carbon. Pseudomonas aeruginosa can utilize at least 80 different organic compounds (41). A mechanism of catabolite repression control exists in these organisms (18) which prevents them from wasting energy maintaining the enzymes for all these catabolic pathways and ensures the preferential utilization of the most efficient source of carbon and energy. Such a regulatory mechanism has also been identified in the enteric bacteria (20) and in Bacillus spp. (6).In the enteric bacteria, the molecular mechanism of catabolite repression control involves a catabolite activator protein (Cap) which, when bound to cyclic AMP (cAMP), interacts with promoter regions of regulated genes to facilitate the binding of RNA polymerase, thereby initiating transcription (20). In the presence of glucose, the cAMP pool is lowered, Cap is not bound, and the regulated genes are not transcribed (i.e., they are repressed). The effect of glucose on cAMP pools is mediated by components of the phosphoenolpyruvate phosphotransferase system which also serve to activate adenylate cyclase (33). Since the initial identification of these regulatory components, catabolite repression has proven to be a global mechanism in the enteric bacteria, affecting at least 28 separate promoters which regulate biosynthetic as well as catabolic operons (7). It also has been found to act as a negative regulator as well as a positive regulator (1,7,23,24).In Bacillus spp. catabolite repression is not mediated by glucose, nor is cAMP involved (6,37,40). Genetic evidence has implicated the catabolite control protein (CcpA), a member of the GalR family of repressor proteins (6), Hpr, a component of the phosphoenolpyruvate phosphotransferase system (9), and a cis-acting DNA sequence (CRE) (15,48). Recent work has shown that HPr specifically phosphorylated at Ser-46 forms a complex wit...