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Eukaryotic Cell, February 2007, p. 262-270, Vol. 6, No. 2
1535-9778/07/$08.00+0     doi:10.1128/EC.00188-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mpt5p, a Stress Tolerance- and Lifespan-Promoting PUF Protein in Saccharomyces cerevisiae, Acts Upstream of the Cell Wall Integrity Pathway

Mark S. Stewart, Sue Ann Krause, Josephine McGhie, and Joseph V. Gray^*

Division of Molecular Genetics, Faculty of Biomedical and Life Sciences, University of Glasgow, Anderson College Complex, 56 Dumbarton Road, Glasgow G11 6NU, United Kingdom

Received 16 June 2006/ Accepted 6 December 2006

Pumilio family (PUF) proteins affect specific genes by binding to, and inhibiting the translation or stability of, their transcripts. The PUF domain is required and sufficient for this function. One Saccharomyces cerevisiae PUF protein, Mpt5p (also called Puf5p or Uth4p), promotes stress tolerance and replicative life span (the maximum number of doublings a mother cell can undergo before entering into senescence) by an unknown mechanism thought to partly overlap with, but to be independent of, the cell wall integrity (CWI) pathway. Here, we found that mpt5 mutants also display a short chronological life span (the time cells stay alive in saturated cultures in synthetic medium), a defect that is suppressed by activation of CWI signaling. We found that Mpt5p is an upstream activator of the CWI pathway: mpt5 mutants display the appropriate phenotypes and genetic interactions, display low basal activity of the pathway, and are defective in activation of the pathway upon thermal stress. A set of mRNAs that specifically bind to Mpt5p was recently reported. One such putative target, LRG1, encodes a GTPase-activating protein for Rho1p that directly links Mpt5p to CWI signaling: Lrg1p inhibits CWI signaling, LRG1 mRNA contains a consensus Mpt5p-binding site in its putative 3' untranslated region, loss of Lrg1p suppresses the temperature sensitivity and CWI signaling defects of mpt5 mutants, and LRG1 mRNA abundance is inhibited by Mpt5p. We conclude that Mpt5p is required for normal replicative and chronological life spans and that the CWI pathway is a key and direct downstream target of this PUF protein.

Published ahead of print on 15 December 2006.

Present address: Standard Life, Standard Life House, 30 Lothian Road, Edinburgh EH1 2DH, United Kingdom.