Potassium is an essential intracellular ion, and its optimum intracellular concentration is crucial for many processes; therefore it is fundamental for cells to regulate K+ uptake and efflux via specialised proteins precisely. The Trk1 protein is one of them. Using yeast cells, we showed that a very short part of the protein, the IL2 loop and its two conserved residues (serine 882 and threonine 900) are essential both for the proper folding of the nascent protein and for the regulation of the protein’s activity in response to changes in the extracellular concentration of potassium ions. The binding of regulatory proteins 14-3-3 to phosphorylated threonine 900 is crucial for this regulation.