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Mol. Cell. Biol. 20 (23): 8826-8835

Copyright © 2000 by the American Society for Microbiology. All rights reserved.

Molecular and Cellular Biology, December 2000, p. 8826-8835, Vol. 20, No. 23
Copyright © 2000, American Society for Microbiology. All rights reserved.

Localization and Signaling of Gbeta Subunit Ste4p Are Controlled by a-Factor Receptor and the a-Specific Protein Asg7p

Jinah Kim,1 Eric Bortz,1 Hualin Zhong,2,dagger Thomas Leeuw,3,Dagger Ekkehard Leberer,3,Dagger Andrew K. Vershon,2 and Jeanne P. Hirsch1,*

Department of Cell Biology and Anatomy, Mount Sinai School of Medicine, New York, New York 100291; Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 088542; and Eukaryotic Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2, Canada3

Received 29 June 2000/Returned for modification 22 August 2000/Accepted 15 September 2000

Haploid yeast cells initiate pheromone signaling upon the binding of pheromone to its receptor and activation of the coupled G protein. A regulatory process termed receptor inhibition blocks pheromone signaling when the a-factor receptor is inappropriately expressed in MATa cells. Receptor inhibition blocks signaling by inhibiting the activity of the G protein beta  subunit, Ste4p. To investigate how Ste4p activity is inhibited, its subcellular location was examined. In wild-type cells, alpha -factor treatment resulted in localization of Ste4p to the plasma membrane of mating projections. In cells expressing the a-factor receptor, alpha -factor treatment resulted in localization of Ste4p away from the plasma membrane to an internal compartment. An altered version of Ste4p that is largely insensitive to receptor inhibition retained its association with the membrane in cells expressing the a-factor receptor. The inhibitory function of the a-factor receptor required ASG7, an a-specific gene of previously unknown function. ASG7 RNA was induced by pheromone, consistent with increased inhibition as the pheromone response progresses. The a-factor receptor inhibited signaling in its liganded state, demonstrating that the receptor can block the signal that it initiates. ASG7 was required for the altered localization of Ste4p that occurs during receptor inhibition, and the subcellular location of Asg7p was consistent with its having a direct effect on Ste4p localization. These results demonstrate that Asg7p mediates a regulatory process that blocks signaling from a G protein beta  subunit and causes its relocalization within the cell.

* Corresponding author. Mailing address: Box 1007, Mount Sinai School of Medicine, 1 Gustave Levy Place, New York, NY 10029. Phone: (212) 241-0224. Fax: (212) 860-1174. E-mail: Jeanne.Hirsch{at}

dagger Present address: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10021.

Dagger Present address: Aventis Biotechnologie, D-82152 Martinsried, Germany.

Molecular and Cellular Biology, December 2000, p. 8826-8835, Vol. 20, No. 23
Copyright © 2000, American Society for Microbiology. All rights reserved.

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