2 GENES FOR CARBOHYDRATE CATABOLISM ARE DIVERGENTLY TRANSCRIBED FROM A REGION OF DNA CONTAINING THE HEXC LOCUS IN PSEUDOMONAS-AERUGINOSA-PAO1

The hexC locus of Pseudamonas aeruginosa PAO1 was localized to a 247-b p 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 act ivities 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 wer e not affected by the presence of the hexC plasmid. Furthermore, the h exC-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 s eparating two divergent open reading frames (ORFs). Transcriptional st art sites for these two genes were mapped to the intergenic region, de monstrating that this sequence contained overlapping divergent promote rs. The intergenic region contained potential regulatory sequences suc h as dyad symmetry motifs, polydeoxyadenosine tracts, and a sequence m atching the integration host factor recognition site in Escherichia co li. One of the ORFs encoded a 610-amino-acid protein with 55 to 60% id entity to 6-phosphogluconate dehydratase from E. coli and Zymomonas mo bilis. The second ORF coded for a protein of 335 amino acids that disp layed 45 to 60% identity to the NAD-dependent glyceraldehyde-3-phospha te dehydrogenase (GAP) family of enzymes. The NAD-dependent GAP gene o n the P. aeruginosa chromosome was previously unmapped. GAP was found to exhibit the hexC-dependent increase in its basal activity, establis hing it as a fifth catabolic enzyme in the multioperonic hex regulon.