Positive regulator of the ben and cat genes for benzoate degradation. BenM is necessary for ben gene expression but not for expression of the cat genes, which can be regulated by CatM. Binds to the inducers cis,cis-muconate and benzoate. Homotetramer; dimer of dimers. The dimers can also associate to form linear, higher oligomers (in vitro). Contains a secondary binding site for benzoate in addition to a primary effector binding site that can accommodate either cis,cis-muconate or benzoate. The existence of this secondary binding site may explain the synergistic effects of cis,cis-muconate and benzoate. Belongs to the LysR transcriptional regulatory family.