Regulatory circuits controlling transcription of TOL plasmid operon encoding meta-cleavage pathway for degradation of alkylbenzoates by Pseudomonas.
TOL plasmid pWWO of Pseudomonas putida contains two operons that specify a pathway for the degradation of aromatic hydrocarbons. The 'upper' operon encodes enzymes for the oxidation of toluene to benzoate and xylenes to toluates, whereas the meta-cleavage operon specifies the further oxidation of benzoate and toluates. Transcription of the upper pathway operon is positively regulated by the XylR protein, which is activated by toluene/xylenes and their alcohol catabolic products, in combination with the NtrA protein, a sigma factor. Expression of the meta-operon is positively controlled by the XylS protein which is activated by meta-pathway substrates, and is independent of NtrA protein. Expression of the meta pathway is also induced by toluene/xylene-activated XylR protein via a cascade regulatory system in which this protein in combination with NtrA protein stimulates transcription from the xylS gene promoter. Hyper-production of XylS protein in turn provokes high level expression of the meta-operon, which is independent of meta-pathway substrates. The two promoters, which are activated by the XylR and NtrA proteins, the upper pathway promoter and the xylS gene promoter, exhibit three regions of homology centred at -12(5'-TTGCATG-3'), -24(5'-TGGCPuT-3') and -45(5'-TAAAATAAGPuPuCGPuTC-3'), with respect to their principal transcription initiation points. The possible physiological significance of activated XylR-protein-induced expression of the meta-operon through amplification of XylS protein levels is considered.
Ramos
J L
JL
Department of Medical Biochemistry, University of Geneva, Switzerland.
Mermod
N
N
Timmis
K N
KN
D001483:Base Sequence; D001565:Benzoates / Q000378:metabolism*; D005796:Genes; D005798:Genes, Bacterial; D005809:Genes, Regulator; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon; D011401:Promoter Regions, Genetic; D011549:Pseudomonas / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D014158:Transcription, Genetic
D001565:Benzoates; D012333:RNA, Messenger