Open AccessYeast Rpi1 Is a Putative Transcriptional Regulator That Contributes to Preparation for Stationary Phase
Author(s) -
Andrew K. Sobering,
Un Sung Jung,
Kyung S. Lee,
David E. Levin
Publication year - 2002
Publication title -
eukaryotic cell
Language(s) - English
Resource type - Journals
eISSN - 1535-9778
pISSN - 1535-9786
DOI - 10.1128/ec.1.1.56-65.2002
Subject(s) - biology , regulator , saccharomyces cerevisiae , protein kinase a , microbiology and biotechnology , signal transduction , gene , point mutation , kinase , cell growth , transcriptional regulation , genetic screen , regulation of gene expression , mutation , gene expression , mutant , genetics
The RPI1 gene of Saccharomyces cerevisiae was identified initially as a dosage suppressor of the heat shock sensitivity associated with overexpression of RAS2 (J. Kim and S. Powers, Mol. Cell. Biol. 11:3894-3904, 1991). Based on its failure to suppress mutationally activated RAS2, RPII was proposed to be a negative regulator of the Ras/cyclic AMP (cAMP) pathway that functions at a point upstream of Ras. We isolated RPI1 as a high-copy-number suppressor of the cell lysis defect associated with a null mutation in the MPK1 gene, which encodes the mitogen-activated protein kinase of the cell wall integrity-signaling pathway. Although the sequence of Rpil is not informative about its function, we present evidence that this protein resides in the nucleus, possesses a transcriptional activation domain, and affects the mRNA levels of several cell wall metabolism genes. In contrast to the previous report, we found that RPI1 overexpression suppresses defects associated with mutational hyperactivation of the Ras/cAMP pathway at all points including constitutive mutations in the cAMP-dependent protein kinase. We present additional genetic and biochemical evidence that Rpil functions independently of and in opposition to the Ras/cAMP pathway to promote preparations for the stationary phase. Among these preparations is a fortification of the cell wall that is antagonized by Ras pathway activity. This observation reveals a novel link between the Ras/cAMP pathway and cell wall integrity. Finally, we propose that inappropriate expression of RPI1 during log phase growth drives fortification of the cell wall and that this behavior is responsible for suppression of the mpkl cell lysis defect.