Regulation by two CatR proteins that differ in binding affinity to catB promoters expressing two cat gene clusters

We isolated the two LysR-type regulatory proteins CatR(1) and CatR(2), whic h regulate the expression of cat(1) and cat(2) gene clusters, respectively, required for catechol degradation in the bacterium Frateuria sp. ANA-18. I n a gel mobility shift assay using CatR(1) and the DNA fragment containing the catB(1) promoter region, the formation of two complexes, complex 1-1 (C 1-1) and complex 1-2 (C1-2), was observed in the presence of cis,cis-mucona te. On the other hand, CatR(2) and the DNA fragment containing the catB(2) promoter region formed only complex 2-2 (C2-2) at a lower concentration of cis,cis-muconate than that at which C1-1 and C1-2 were formed. As the conce ntration of cis, cis-muconate decreased, the production of the muconate cyc loisomerase isozyme MC II encoded by catB(2) decreased as well as that of M C I encoded by catB(1). However, the amount of MC II synthesized was larger than that of MC I at low concentrations. On the basis of these results, we concluded that the catB(2) promoter was activated at low concentrations of cis,cis-muconate.