REGULATION OF THE PCAIJ GENES FOR AROMATIC ACID DEGRADATION IN PSEUDOMONAS-PUTIDA

Six of the genes encoding enzymes of the beta-ketoadipate pathway for benzoate and 4-hydroxybenzoate degradation in Pseudomonas putida are o rganized into at least three separate transcriptional units. As an ini tial step to defining this pca regulon at the molecular level, lacZ fu sions were made with the pcaI and pcaJ genes, which encode the two sub units of beta-ketoadipate:succinyl-coenzyme A transferase, the enzyme catalyzing the next-to-last step in the beta-ketoadipate pathway. Fusi on analyses showed that pcaI and pcaJ constitute an operon which requi res beta-ketoadipate or its nonmetabolizable analog, adipate, as well as the pcaR regulatory gene for induction. The pcaIJ promoter is likel y to be a sigma-type promoter; it has a sigma70-type consensus sequenc e and did not require the alternative sigma factor, RpoN, for inductio n. Deletion analysis of the promoter region of a pcaI-lacZ transcripti onal fusion indicated that no specific DNA sequences upstream of the - 35 region were required for full induction. This implies that the bind ing site for the activator protein, PcaR, is unusually close to the tr anscriptional start site of pcaIJ.