Represses expression of the HQNO methyltransferase htm gene (Rv0560c) by binding to its promoter region (PubMed:26303802, PubMed:27432954, PubMed:28743871). Also represses the expression of at least five other genes, including the methyltransferase Rv0558 (PubMed:26303802). Binds salicylate (SA), para-aminosalicylic acid (PAS) and gemfibrozil (PubMed:28743871). Binding of effector molecule SA, or its structural analog PAS, to the binding pocket of Rv2887 induces conformational change in its DNA binding domain, preventing binding to the promoter region of htm, triggering the expression of this SAM-dependent methyltransferase. Homodimer. Conformational changes take place in the N-terminal and the winged-HTH (wHTH) domain on ligand or DNA binding. SA and PAS stabilize a conformation of Rv2887 incompatible with DNA binding. Rotation of the N-terminal plays a key role in the dimerization. Mutation of the gene leads to derepression and increased expression of htm (PubMed:27432954). Inactivation of the gene confers resistance to the imidazo[1,2-a]pyridine-4-carbonitrile-based agent MP-III-71, an effective antimycobacterial compound that shows no cross-resistance to existing antituberculosis drugs (PubMed:26303802).