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Molecular and Cellular Biology, August 2007, p. 5725-5736, Vol. 27, No. 16
0270-7306/07/$08.00+0     doi:10.1128/MCB.01375-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Key Role for Intracellular K+ and Protein Kinases Sat4/Hal4 and Hal5 in the Plasma Membrane Stabilization of Yeast Nutrient Transporters{triangledown}

Jorge Pérez-Valle,1,{dagger} Huw Jenkins,1,{dagger} Stephanie Merchan,1 Vera Montiel,2 José Ramos,2 Sukesh Sharma,3 Ramón Serrano,1 and Lynne Yenush1*

Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-CSIC, 46022 Valencia, Spain,1 Departamento de Microbiología, Edificio Severo Ochoa, Campus de Rabanales, Universidad de Córdoba, 14080 Córdoba, Spain,2 Department of Biochemistry, Panjab University, Chandigarh 160014, India3

Received 27 July 2006/ Returned for modification 5 September 2006/ Accepted 21 May 2007

K+ transport in living cells must be tightly controlled because it affects basic physiological parameters such as turgor, membrane potential, ionic strength, and pH. In yeast, the major high-affinity K+ transporter, Trk1, is inhibited by high intracellular K+ levels and positively regulated by two redundant "halotolerance" protein kinases, Sat4/Hal4 and Hal5. Here we show that these kinases are not required for Trk1 activity; rather, they stabilize the transporter at the plasma membrane under low K+ conditions, preventing its endocytosis and vacuolar degradation. High concentrations (0.2 M) of K+, but not Na+ or sorbitol, transported by undefined low-affinity systems, maintain Trk1 at the plasma membrane in the hal4 hal5 mutant. Other nutrient transporters, such as Can1 (arginine permease), Fur4 (uracil permease), and Hxt1 (low-affinity glucose permease), are also destabilized in the hal4 hal5 mutant under low K+ conditions and, in the case of Can1, are stabilized by high K+ concentrations. Other plasma membrane proteins such as Pma1 (H+-pumping ATPase) and Sur7 (an eisosomal protein) are not regulated by halotolerance kinases or by high K+ levels. This novel regulatory mechanism of nutrient transporters may participate in the quiescence/growth transition and could result from effects of intracellular K+ and halotolerance kinases on membrane trafficking and/or on the transporters themselves.

* Corresponding author. Mailing address: Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-CSIC, Camino de Vera s/n, 46022 Valencia, Spain. Phone: 34 96 387 7860. Fax: 34 96 387 7859. E-mail: lynne{at}ibmcp.upv.es

{triangledown} Published ahead of print on 4 June 2007.

{dagger} These authors contributed equally to the work.

Molecular and Cellular Biology, August 2007, p. 5725-5736, Vol. 27, No. 16
0270-7306/07/$08.00+0     doi:10.1128/MCB.01375-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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