Physical mapping of the K+ transport trkA gene of Escherichia coli and overproduction of the TrkA protein

The position on the Escherichia coli chromosome of trkA, a gene coding for a membrane protein involved in K+ transport by the constitutive uptake system Trk, was determined. We observed that the gene is transcribed in a clockwise direction and that it is located at 72.4 min on the chromosome in a 1.75-kilobase NruI-EcoRV DNA fragment 1.0 kilobase upstream of rplQ. We localized an additional gene encoding a 17,000-molecular-weight protein of unknown function between the trkA and rplQ genes. A plasmid, pDB3, was constructed in which the transcription of the trkA gene was put under the control of the lambda pL promoter. pDB3-containing cells of a strain, which contained the temperature-sensitive lambda repressor cI857 in the chromosome, overproduced the 53,000-molecular-weight TrkA protein at the nonpermissive temperature to such an extent that TrkA became the major cell protein. From cell fractionation studies, we conclude that the overproduced TrkA protein forms aggregates.