DNase I footprinting, DNA bending and in vitro transcription analyses of ClcR and CatR interactions with the clcABD promoter: evidence of a conserved transcriptional activation mechanism.

In Pseudomonas putida, benzoate and 3-chlorobenzoate are converted to catechol and 3-chlorocatechol, respectively, which are then catabolized to tricarboxylic acid cycle intermediates via the catBCA and clcABD pathways. The catBCA and clcABD operons are regulated by homologous transcriptional activators CatR and ClcR. Previous studies have demonstrated that in addition to sequence similarities, CatR and ClcR share functional similarities which allow catR to complement clcR. In this study, we demonstrate that CatR activates the clcABD promoter in vitro without inducer, but more transcript is produced when inducer is added. DNase I footprinting and DNA-bending analyses demonstrate that CatR binds to and bends the clcABD promoter to the same angle as does ClcR plus its inducer, 2-chloromuconate. This implies that CatR binds to the clc promoter in its active conformation. Transcription of the clcABD promoter by the alpha-subunit truncation mutant (alpha-235) of RNA polymerase was sharply reduced, indicating that the alpha-subunit C-terminal domain is important. However, a small amount of transcript was produced under these conditions, indicating that other contact sites on the RNA polymerase may play a role in activation.