Membrane hyperpolarization and salt sensitivity induced by deletion of PMP3, a highly conserved small protein of yeast plasma membrane

Yeast plasma membranes contain a small 55 amino acid hydrophobic polypeptid e, Pmp3p, which has high sequence similarity to a novel family of plant pol ypeptides that are overexpressed under high salt concentration or low tempe rature treatment. The PMP3 gene is not essential under normal growth condit ions. However, its deletion increases the plasma membrane potential and con fers sensitivity to cytotoxic cations, such as Na+ and hygromycin B. Intere stingly, the disruption of PMP3 exacerbates the NaCl sensitivity phenotype of a mutant strain lacking the Pmr2p/Enap Na+-ATPases and the Nha1p Na+/Hantiporter, and suppresses the potassium dependency of a strain lacking the K+ transporters, Trk1p and Trk2p. All these phenotypes could be reversed b y the addition of high Ca2+ concentration to the medium. These genetic inte ractions indicate that the major effect of the PMP3 deletion is a hyperpola rization of the plasma membrane potential that probably promotes a nonspeci fic influx of monovalent cations. Expression of plant RCI2A in yeast could substitute for the loss of Pmp3p, indicating a common role for Pmp3p and th e plant homologue.