Dual-function repressor/activator of the chbBCARFG operon. In the absence of the inducing sugar chitobiose, together with NagC, represses the chbBCARFG operon for the uptake and metabolism of chitobiose. In association with Crp, and probably in the presence of chitobiose 6-phosphate, induces the transcription of the chbBCARFG operon. Homodimer. By N,N'-diacetylchitobiose. Under prolonged growth on cellobiose as the sole carbon source, spontaneous mutations in chbR and nagC alter the regulation of the chbBCARFG operon, allowing the uptake and metabolism of cellobiose. The mutated regulator makes stronger contact with the target DNA sequence within the chb promoter and has enhanced recognition of cellobiose 6-phosphate as an inducer.