Central regulator of manganese homeostasis that regulates the expression of both manganese uptake and efflux systems (PubMed:27748968, PubMed:10760146, PubMed:12950915). In the presence of high levels of manganese, it mediates repression of the manganese uptake systems MntH and MntABCD and activation of the efflux systems MneP and MneS. Binds with high affinity to the regulatory regions of its target genes (PubMed:27748968, PubMed:12950915). The manganese concentration required for activation of efflux is higher than that for repression of uptake (PubMed:27748968). DNA binding is strongly activated by Mn(2+) and Cd(2+), but it is poorly activated by non-cognate metal cations, including Co(2+), Fe(2+), Ni(2+), Ca(2+) and Zn(2+). In the strict absence of divalent transition metal ions, MntR has a low affinity for DNA. Homodimer. Contains an N-terminal DNA-binding domain and a C-terminal dimerization domain (PubMed:12847518, PubMed:16533030, PubMed:23298157). Contains two metal binding sites per subunit, site A (corresponding to metal ion 2) and site C (corresponding to metal ion 1), which both contribute to the metal selectivity of MntR. A large metal cation is needed at the A site to correctly orient and position the C site ligands. Smaller, non-cognate metal cations bind at the A site, but disrupt the C site, blocking the full activation of MntR. Binding at the C site also favors Mn(2+) and Cd(2+) over other metals (PubMed:16533030, PubMed:23298157). Null mutant is very sensitive to manganese (PubMed:27748968, PubMed:10760146). Mutant also displays increased sensitivity to cadmium (PubMed:10760146). Belongs to the DtxR/MntR family. Was originally thought to act as an activator for the mntABCD operon.