SUBCLONING, NUCLEOTIDE-SEQUENCE, AND EXPRESSION OF TRKG, A GENE THAT ENCODES AN INTEGRAL MEMBRANE-PROTEIN INVOLVED IN POTASSIUM UPTAKE VIA THE TRK SYSTEM OF ESCHERICHIA-COLI

Abstract

The trkG gene encodes a component of the K+ uptake system Trk and is located at 30.5 min inside the lambdoid prophage region rac of the Escherichia coli chromosome. trkG was subcloned, its nucleotide sequence was determined, and its product was identified in a minicell system. The open reading frame of 1,455 bp encodes a hydrophobic membrane protein with a calculated molecular weight of 53,493 that is predicted to contain up to 12 transmembrane helices. The trkG gene product behaved as a hydrophobic membrane protein; it was found exclusively in the membrane fraction of the minicells and its migration in sodium dodecyl sulfate-polyacrylamide gel electrophoresis was anomalous, indicating an apparent molecular weight of 35,000. The trkG gene contains an exceptionally high proportion of infrequently used codons, raising the question of the origin of this gene. trkG does not appear to be a prophage gene since no similarity was observed between the nucleotide sequence of trkG or the amino acid sequence of its product and the sequences of genes or proteins from bacteriophage lambda.