E.coli possesses several transporters for the active uptake of K⁺. Of these, Kdp is a P-type ATPase comprised of three major polypeptide subunits (KdpA,KdpB and KdpC) encoded by genes of the kdp operon, and is the only one whose synthesis is induced at the level of transcription under K^+- limiting growth conditions. Our group had shown that the kdp operon is induced during steady-state growth by ionic solutes such as NaCl but not by non-ionic solutes such as sucrose (1); these and other findings have led us to argue that the signal regulating kdp expression is not turgor as was previously believed, but perhaps the rate of transmembrane K⁺ flux (2). Recently, we have shown that cytoplasmic thiol oxidation status as well as the H-NS protein are also involved in regulating kdp transcription in vivo (3). We have also obtained evidence to suggest that an N-terminal fragment of KdpA, comprising less than one-third of the length of the native polypeptide, is sufficient to confer a membrane potential-driven uptake of K⁺ in vivo, even in the absence of the other two subunits KdpB and KdpC (4). Our current interests are in further understanding the mechanism of K⁺ transport through Kdp as well as its transcriptional regulation.

1. Gowrishankar, J. 1985. Identification of osmoresponsive genes in Escherichia coli: evidence for participation of potassium and proline transport systems in osmoregulation. J. Bacteriol. 164: 434-445.
2. Asha, H., and J. Gowrishankar. 1993. Regulation of kdp operon expression in Escherichia coli: evidence against turgor as signal for transcriptional control. J. Bacteriol. 175: 4528-4537.
3. Sardesai, A. A., and J. Gowrishankar. 2001. trans-Acting mutations in loci other than kdpDE that affect kdp operon regulation in Escherichia coli: effects of cytoplasmic thiol oxidation status and nucleoid protein H-NS on kdp expression. J. Bacteriol. 183: 86-93.
4. Sardesai, A. A., and J. Gowrishankar. 2001. Improvement in K^+- limited growth rate associated with expression of N-terminal fragment of one subunit (KdpA) of the multi-subunit Kdp transporter in Escherichia coli. J. Bacteriol. 183:3515-3520.