Two genes for carbohydrate catabolism are divergently transcribed from a region of DNA containing the hexC locus in Pseudomonas aeruginosa PAO1.
The hexC locus of Pseudomonas aeruginosa PAO1 was localized to a 247-bp segment of chromosomal DNA on the multicopy broad-host-range vector pRO1614. The presence of this plasmid (pPZ196) in strain PAO1 produced the so-called "hexC effect," a two- to ninefold increase in the activities of four carbohydrate catabolism enzymes, glucokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydratase, and 2-keto-3-deoxy-6-phosphogluconate aldolase. The extent of the hexC effect was restricted, since three independently regulated metabolic enzymes were not affected by the presence of the hexC plasmid. Furthermore, the hexC-containing plasmid did not suppress catabolite repression control. Nucleotide sequence analysis of the segment of DNA encompassing hexC revealed a 128-bp region rich in adenosine-plus-thymine (AT) content separating two divergent open reading frames (ORFs). Transcriptional start sites for these two genes were mapped to the intergenic region, demonstrating that this sequence contained overlapping divergent promoters. The intergenic region contained potential regulatory sequences such as dyad symmetry motifs, polydeoxyadenosine tracts, and a sequence matching the integration host factor recognition site in Escherichia coli. One of the ORFs encoded a 610-amino-acid protein with 55 to 60% identity to 6-phosphogluconate dehydratase from E. coli and Zymomonas mobilis. The second ORF coded for a protein of 335 amino acids that displayed 45 to 60% identity to the NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (GAP) family of enzymes. The NAD-dependent GAP gene on the P. aeruginosa chromosome was previously unmapped. GAP was found to exhibit the hexC-dependent increase in its basal activity, establishing it as a fifth catabolic enzyme in the multioperonic hex regulon.
Temple
L
L
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond 23298.
Sage
A
A
Christie
G E
GE
Phibbs
P V
PV
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D050260:Carbohydrate Metabolism; D005798:Genes, Bacterial / Q000235:genetics*; D005942:Gluconates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics; D006836:Hydro-Lyases / Q000235:genetics; D034982:Integration Host Factors; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D018085:Regulon / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D005942:Gluconates; D034982:Integration Host Factors; C440503:integration host factor, Pseudomonas; D009243:NAD; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D006836:Hydro-Lyases; C022362:phosphogluconate dehydratase; D005947:Glucose; C030691:gluconic acid