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First published online May 4, 2004
doi: 10.1242/10.1242/jcs.01050

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Yeast ARL1 encodes a regulator of K⁺ influx

Department of Biology, 406 Reiss Science Center, Box 571229, Georgetown University, Washington, DC 20057, USA

^* Author for correspondence (e-mail: rosenwaa{at}georgetown.edu)

Accepted 9 December 2003

A molecular genetic approach was undertaken in Saccharomyces cerevisiae to examine the functions of ARL1, encoding a G protein of the Ras superfamily. We show here that ARL1 is an important component of the control of intracellular K⁺. The arl1 mutant was sensitive to toxic cations, including hygromycin B and other aminoglycoside antibiotics, tetramethylammonium ions, methylammonium ions and protons. The hygromycin-B-sensitive phenotype was suppressed by the inclusion of K⁺ and complemented by wild-type ARL1 and an allele of ARL1 predicted to be unbound to nucleotide in vivo. The arl1 mutant strain internalized 25% more [¹⁴C]-methylammonium ion than did the wild type, consistent with hyperpolarization of the plasma membrane. The arl1 strain took up 30-40% less ⁸⁶Rb⁺ than did the wild type, showing an inability to regulate K⁺ import properly, contributing to membrane hyperpolarity. By contrast, K⁺ and H⁺ efflux were undisturbed. The loss of ARL1 had no effect on the steady-state level or the localization of a tagged version of Trk1p. High copy suppressors of the hygromycin-B phenotype included SAP155, encoding a protein that interacts with the cell cycle regulator Sit4p, and HAL4 and HAL5, encoding Ser/Thr kinases that regulate the K⁺-influx mediators Trk1p and Trk2p. These results are consistent with a model in which ARL1, via regulation of HAL4/HAL5, governs K⁺ homeostasis in cells.

Key words: Guanine nucleotide-binding protein, Ion homeostasis, Membrane potential, PMA1, TRK1

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