The carbazole-degradative plasmid pCAR1 of Pseudomonas resinovorans strain CA10 has two gene clusters, carAaAaBaBbCAcAdDFE and antABC, which are involved in the conversions of carbazole to anthranilate and anthranilate to catechol, respectively. We proved that the antABC gene cluster, encoding two-component anthranilate 1,2-dioxygenase, constitutes a single transcriptional unit through Northern hybridization and reverse transcription-PCR (RT-PCR) analyses. The transcription start point of antA was mapped at 53 bp upstream point of its translation start point, and the ؊10 and ؊35 boxes were homologous to conserved 70 recognition sequence. Hence the promoter of the ant operon was designated P ant . 5 Deletion analyses using luciferase as a reporter showed that the region up to at least 70 bp from the transcription start point of antA was necessary for the activation of P ant . Luciferase expression from P ant was induced by anthranilate itself, but not by catechol. Two probable AraC/XylS-type regulatory genes found on pCAR1, open reading frame 22 (ORF22) and ORF23, are tandemly located 3.2 kb upstream of the antA gene. We revealed that the product of ORF23, designated AntR, is indispensable for the stimulation of P ant in Pseudomonas putida cells. Northern hybridization and RT-PCR analyses revealed that another copy of P ant , which is thought to be translocated about 2.1 kb upstream of the carAa gene as a consequence of the transposition of ISPre1, actually drives transcription of the carAa gene in the presence of anthranilate, indicating that both ant and car operons are simultaneously regulated by AntR.Among the toxic and persistent compounds that have been released in the environment by human action, the aromatic compounds are of major concern. In spite of their recalcitrance to degradation by most organisms, bacterial strains have adapted to them in consequence of the acquisition of the necessary catabolic abilities to utilize aromatic compounds, and thus rapidly adapting bacteria are regarded as the experimental systems of choice in understanding how catabolic genes end up with regulated expression (8).Carbazole is a recalcitrant N-heterocyclic aromatic compound derived from coal tar and shale oil and possesses mutagenic and toxic activity (1). Pseudomonas resinovorans strain CA10, a gram-negative bacterium isolated from activated sludge, degrades carbazole as the sole source of carbon, nitrogen, and energy (27). In strain CA10, carbazole is initially converted into anthranilate and 2-hydroxypenta-2,4-dienoate through a three-step upper pathway catalyzed by carbazole 1,9a-dioxygenase (CarA), the meta-cleavage enzyme (CarB), and the meta-cleavage compound hydrolase (CarC) (Fig. 1A) (32,33). CarA is a multicomponent dioxygenase system composed of terminal oxygenase component CarAa, ferredoxin component CarAc, and ferredoxin reductase component CarAd. meta-Cleavage enzyme CarB is a heterotetrameric enzyme (␣ 2  2 ) composed of CarBa and CarBb subunits. The resulting metabolite, anthranilate, is a naturally occ...