ESCHERICHIA-COLI POSSESSES 2 HOMOLOGOUS ANAEROBIC C-4-DICARBOXYLATE MEMBRANE TRANSPORTERS (DCUA AND DCUB) DISTINCT FROM THE AEROBIC DICARBOXYLATE TRANSPORT-SYSTEM (DCT)

The nucleotide sequences of two Escherichia coli genes, dcuA and dcuB (formerly designated genA and genF), have been shown to encode highly homologous products, M(r) 45,751 and 47,935 (434 and 446 amino acid re sidues) with 36% sequence identity (63% similarity). These proteins ha ve a high proportion (similar to 61%) of hydrophobic residues and are probably members of a new group of integral inner membrane proteins. T he Locations of the dcu genes, one upstream of the aspartase gene (dcu A-aspA) and the other downstream of the anaerobic fumarase gene (fumB- dcuB), suggested that they may function in the anaerobic transport of C-4-dicarboxylic acids. Growth tests and transport studies with mutant s containing insertionally inactivated chromosomal dcuA and dcuB genes show that their products perform analogous and mutually complementary roles as anaerobic dicarboxylate carriers. The anaerobic dicarboxylat e transport systems (Dcu) are genetically and functionally distinct fr om the aerobic system (Dct).