Identification of a third secondary carrier (DcuC) for anaerobic C-4-dicarboxylate transport in Escherichia coli: Roles of the three Dcu carriers in uptake and exchange

In Escherichia coli, two carriers (DcuA and DcuB) for the transport of C-4 dicarboxylates in anaerobic growth were known, Here a novel gene dcuC was identified encoding a secondary carrier (DcuC) for C-4 dicarboxylates which is functional in anaerobic growth. The dcuC gene is located at min 14.1 of the E. coli map in the counterclockwise orientation. The ducC gene combines two open reading frames found in other strains off. coli K-12, The gene product (DcuC) is responsible for the transport of C-4 dicarboxylates in DcuA-DcuB-deficient cells, The triple mutant (dcuA dcuB dcuC) is completely devoid of C-4-dicarboxylate transport (exchange and uptake) during anaerobic growth, and the bacteria are no longer capable of growth by fumarate respiration, DcuC, however, is not required for C-4-dicarboxylate uptake in aerobic growth, The dcuC gene encodes a putative protein of 461 amino acid residues with properties typical for secondary procaryotic carriers, DcuC shows sequence similarity to the two major anaerobic C-4-dicarboxylate carriers DcuA and DcuB. Mutants producing only DcuA, DcuB, or DcuC were prepared, In the mutants, DcuA, DcuB, and DcuC were each able to operate in the exchange and uptake mode.