In Saccharomyces cerevisiae, Snf1 protein kinase of the Snf1/AMP-activated protein kinase family is required for growth on nonfermentable carbon sources and nonpreferred sugars. Three kinases, Pak1, Elm1, and Tos3, activate Snf1 by phosphorylation of its activation-loop threonine, and the absence of all three causes the Snf(-) phenotype. No phenotype has previously been reported for the tos3Delta single mutation. We show here that, when cells are grown on glycerol-ethanol, tos3Delta reduces growth rate, Snf1 catalytic activity, and activation of the Snf1-dependent carbon source-responsive element (CSRE) in the promoters of gluconeogenic genes. In contrast, tos3Delta did not significantly affect Snf1 catalytic activity or CSRE function during abrupt glucose depletion, indicating that Tos3 has a more substantial role in activating Snf1 protein kinase during growth on a nonfermentable carbon source than during acute carbon stress. We also report that Tos3 is localized in the cytosol during growth in either glucose or glycerol-ethanol. These findings lend support to the idea that the Snf1 protein kinase kinases make different contributions to cellular regulation under different growth conditions.

• PMID: 15879520
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Journal Article | Research Support, N.I.H., Extramural | Research Support, Non-U.S. Gov't | Research Support, U.S. Gov't, P.H.S.

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Kim MD, Hong SP, Carlson M

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