Subunit structure of nonheme iron-containing dioxygenases

Sequence of the plasmid-encoded catechol 1,2-dioxygenase-expressing gene, pheB, of phenol-degrading Pseudomonas sp. strain EST1001

Phenol monooxygenase (PMO) and catechol 1,2-dioxygenase (C12O), the two first enzymes of the phenol-degradation pathways, are encoded by a 3.4-kb DNA fragment cloned from Pseudomonas sp. EST1001 plasmid DNA. We have previously shown that activation of the cloned genes in Pseudomonas putida PaW85 is controlled by insertion of the 17-kb transposon, Tn4652, from the host chromosome into the plasmid carrying these genes [Kivisaar et al. Plasmid 24 (1990) 25-36]. Transcription of the DNA encoding PMO (pheA) and C12O (pheB) is activated by a promoter located on a 0.2-kb SacI-ClaI fragment from Tn4652. We have determined the nucleotide sequence of pheB. The 906-bp gene encodes a protein product with a deduced Mr of 33,362. The relationship between the pheB gene and other C12O-encoding genes has been shown: comparison of the pheB sequence with sequences of catA of Alcaligenes calcoaceticus, tfdC of A. eutrophus and clcA of P. putida demonstrated that there are conserved residues in all the four protein products of these genes.

Cloning and expression of the catA and catBC gene clusters from Pseudomonas aeruginosa PAO

A 9.9-kilobase (kb) BamHI restriction endonuclease fragment encoding the catA and catBC gene clusters was selected from a gene bank of the Pseudomonas aeruginosa PAO1c chromosome. The catA, catB, and catC genes encode enzymes that catalyze consecutive reactions in the catechol branch of the beta-ketoadipate pathway: catA, catechol-1,2-dioxygenase (EC 1.13.11.1); catB, muconate lactonizing enzyme (EC 5.5.1.1); and catC, muconolactone isomerase (EC 5.3.3.4). A recombinant plasmid, pRO1783, which contains the 9.9-kb BamHI restriction fragment complemented P. aeruginosa mutants with lesions in the catA, catB, or catC gene; however, this fragment of chromosomal DNA did not contain any other catabolic genes which had been placed near the catA or catBC cluster based on cotransducibility of the loci. Restriction mapping, deletion subcloning, and complementation analysis showed that the order of the genes on the cloned chromosomal DNA fragment is catA, catB, catC. The catBC genes are tightly linked and are transcribed from a single promoter that is on the 5' side of the catB gene. The catA gene is approximately 3 kb from the catBC genes. The cloned P. aeruginosa catA, catB, and catC genes were expressed at basal levels in blocked mutants of Pseudomonas putida and did not exhibit an inducible response. These observations suggest positive regulation of the P. aeruginosa catA and catBC cluster, the absence of a positive regulatory element from pRO1783, and the inability of the P. putida regulatory gene product to induce expression of the P. aeruginosa catA, catB, and catC genes.