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J. Biol. Chem., Vol. 278, Issue 23, 20638-20644, June 6, 2003

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The C-terminal Tail Preceding the CAAX Box of a Yeast G Protein Subunit Is Dispensable for Receptor-mediated G Protein Activation in Vivo^*

Sharon L. Chinault and Kendall J. Blumer 

From the Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110

The subunits of heterotrimeric G proteins are required for receptor-G protein coupling. The C-terminal domains of G subunits can contact receptors and influence the efficiency of receptor-G protein coupling in vitro. However, it is unknown whether receptor interaction with the C terminus of G is required for signaling in vivo. To address this question, we cloned G homologs with diverged C-terminal sequences from five species of budding yeast. Each G homolog functionally replaced the G subunit of the yeast Saccharomyces cerevisiae (STE18 gene product). Mutagenesis of S. cerevisiae Ste18 likewise indicated that specific C-terminal sequence motifs are not required for signaling. Strikingly, an internal in-frame deletion removing sequences preceding the C-terminal CAAX box of Ste18 did not impair signaling by either of its cognate G protein-coupled pheromone receptors. Therefore, receptor interaction with the C-terminal domain of yeast G is not required for receptor-mediated G protein activation in vivo. Because the mechanism of G protein activation by receptors is conserved from yeast to humans, mammalian receptors may not require interaction with the tail of G for G protein activation in vivo. However, receptor-G interaction may modulate the efficiency of receptor-G protein coupling or promote activation of G effectors that co-cluster with receptors.

Received for publication, December 12, 2002 , and in revised form, March 24, 2003.

^* This work was supported in part by National Institutes of Health Grant GM44592 (to K. J. B.) and by an American Heart Association Predoctoral Fellowship (to S. L. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Cell Biology and Physiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110. Tel.: 314-362-1668; Fax: 314-362-7463; E-mail: kblumer{at}cellbio.wustl.edu.

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