Member of the two-component regulatory system DcuR/DcuS. Involved in the C4-dicarboxylate-stimulated regulation of the genes encoding the anaerobic fumarate respiratory system (frdABCD; nuoAN; dcuB; dcuC; sdhCDAB; etc.). Weakly regulates the aerobic C4-dicarboxylate transporter dctA (By similarity). Phosphorylated and activated by DcuS.