Transcriptional regulator involved in the activation of the purU-mabO-folD-nepA-nepB and mao-ORF55-nbr operons implicated in the nicotine catabolic pathway. The sequence GTTT-14 bp-AAAC seems to be the core binding site of the regulator upstream of the -35 promoter region of the operon. Alkaloid degradation; nicotine degradation [regulation]. Forms oligomers in solution, probably homotetramers. Cells lacking this gene do not produce the MabO protein in the presence of nicotine, in contrast to the wild-type. Transcription of the nepAB genes and of the mao-ORF55-nbr operon is abolished in the mutant strain.