Mapping, cloning, expression, and sequencing of the rhaT gene, which encodes a novel L-rhamnose-H+ transport protein in Salmonella typhimurium and Escherichia coli.

A L-rhamnose transport-negative strain of Escherichia coli was generated by Mu d(ApR,lac)I mutagenesis. This strain was used to isolate a clone of Salmonella typhimurium DNA that encoded L-rhamnose-H+ transport activity, the gene for which, rhaT, was sequenced. The rhaT gene was mapped on the E. coli chromosome between rhaR and sodA at 87.9 min, initially by Southern blot analysis and then by the isolation, expression, and sequencing of the rhaT gene. Both rhaT genes encoded a hydrophobic protein of 344 amino acids (91% identical) that contained 10 putative transmembrane regions. The RhaT protein represents a novel class of sugar transport protein.