Transcriptional Activation of Quinoline Degradation Operons of Pseudomonas putida 86 by the AraC/XylS-Type Regulator OxoS and Cross-Regulation of the P qorM Promoter by XylS

Abstract

ABSTRACT The quinoline-degradative gene cluster ( oxoO , open reading frames 1 to 6 [ORF1 to -6], qorMSL , ORF7 to -9, oxoR ) of Pseudomonas putida 86 consists of several overlapping operons controlled in response to quinoline by the master promoter P oxoO and internal promoters Porf3, P qorM , and P oxoR . ORF7 to -9, presumed to be important for maturation of the molybdenum hydroxylase quinoline 2-oxidoreductase, are also weakly transcribed independently of quinoline. Expression of the oxoS gene, located upstream of oxoO , is not influenced by the carbon source. OxoS shows 26% amino acid sequence identity to XylS, the transcriptional regulator of the meta pathway promoter Pm of TOL plasmid pWW0, and is required for quinoline-dependent transcription from P oxoO , Porf3, P qorM , and P oxoR . 5′ deletion analysis of P oxoO and P qorM suggested that a 5′-TGCPuCT-N 3 -GGGATA-3′ motif, which resembles the distal 5′-TGCA-N 6 -GGNTA-3′ half-site of the tandem XylS binding site, is essential for oxoS -dependent transcriptional activation. P qorM , which shows similarity to the tandem XylS recognition site of Pm, was cross-activated by the xylS gene product in response to benzoate. The distal half-site of P qorM is necessary, but probably not sufficient, for transcriptional activation by XylS. Despite conservation in P oxoO of a distal 5′-TGCA-N 6 -GGNTA-3′ sequence, cross-activation of P oxoO by XylS and benzoate was not observed. The oxoS gene product in the presence of quinoline weakly stimulated transcription from the Pm promoter. Involvement of an XylS-type protein in the regulation of genes encoding synthesis of a molybdenum hydroxylase is without precedent and may reflect the evolutionary origin of this pathway in the metabolism of aromatic compounds.