Responsible for the low-affinity transport of potassium into the cell, with the probable concomitant uptake of protons (symport system). Can also transport cesium. Kup is probably the major potassium uptake system upon hyper-osmotic stress at a low pH. Uptake is inhibited by protonophores such as CCCP. Belongs to the HAK/KUP transporter (TC 2.A.72) family.