To assess the physiological function of Ca(2+)‐dependent protein phosphatase (PP2B) in the yeast Saccharomyces cerevisiae, the phenotypes of PP2B‐deficient mutants were investigated. Although PP2B was dispensable for growth under normal conditions, the mutations did, however, cause growth inhibition under certain stress circumstances. The growth of the mutants was inhibited by NaCl and LiCl, but not by KCl, CaCl2, MgCl2 or nonspecific osmotic stresses. Upon shift to high NaCl medium, intracellular Na+ levels of both wild type yeast and the mutants initially increased at a comparable rate. However, internal Na+ in wild type cells started to decline more rapidly than the mutant cells during cultivation in high NaCl medium, indicating that PP2B is important in maintaining a gradient across the membrane. The protection against salt stress was achieved, at least in part, by the stimulation of Na+ export. The maintenance of a high level of internal K+ in high NaCl medium was also PP2B‐dependent. In the presence of the immunosuppressant FK506, the growth behaviour and intracellular Na+ and K+ of wild type cells in high NaCl medium became very similar to those of the PP2B‐deficient mutant in a manner dependent on the presence of the FK506 binding protein.
Signalling via calcium is probably involved in regulating eukaryotic cell proliferation, but details of its mechanism of action are unknown. In Schizosaccharomyces pombe, the onset of mitosis is determined by activation of a complex of the p34cdc2 protein kinase and a cyclin protein that is specific to the G2 phase of the cell cycle. This activation requires dephosphorylation of p34cdc2. Weel, a tyrosine kinase that inhibits p34cdc2 by phosphorylating it, is needed to determine the length of G2 phase. Here we show that calcium-activated pathways in Saccharomyces cerevisiae control the onset of mitosis by regulating Swel, a Weel homologue. Zds1 (also known as Oss1 and Hst1) is important in repressing the transcription of SWE1 in G2 phase. In the presence of high calcium levels, cells lacking Zds1 are delayed in entering mitosis. Calcineurin and Mpk1 regulate Swel activation at the transcriptional and posttranslational levels, respectively, and both are required for the calcium-induced delay in G2 phase. These cellular pathways also induce a G2-phase delay in response to hypotonic shock.
A secretory defect causes specific and significant transcriptional repression of both ribosomal protein and rRNA genes (K. Mizuta and J. R. Warner, Mol. Cell. Biol. 14:2493-2502, 1994), suggesting the coupling of plasma membrane and ribosome syntheses. In order to elucidate the molecular mechanism of the signaling pathway, we isolated a cold-sensitive mutant with a mutation in a gene termed RRS1 (regulator of ribosome synthesis), which appeared to be defective in the signaling pathway. The rrs1-1 mutation greatly reduced transcriptional repression of both rRNA and ribosomal protein genes that is caused by a secretory defect. RRS1 is a novel, essential gene encoding a nuclear protein of 203 amino acid residues that is conserved in eukaryotes. A conditional rrs1-null mutant was constructed by placing RRS1 under the control of the GAL1 promoter. Rrs1p depletion caused defects in processing of pre-rRNA and assembly of ribosomal subunits.Balanced synthesis of cellular components is required for normal cell growth. A temperature-sensitive mutation in SLY1, whose gene product is involved in endoplasmic reticulum-toGolgi trafficking (26), causes the transcriptional repression of both ribosomal protein and rRNA genes in Saccharomyces cerevisiae (20). Further examination using various sec mutants showed that a defect anywhere in the secretory pathway, from a step prior to insertion of the nascent peptide into the endoplasmic reticulum to a step involved in the formation of the plasma membrane, prevents the continued synthesis of the components of the ribosome. Similar results were obtained following treatment of wild-type cells with the secretory inhibitors tunicamycin and brefeldin A (20). Furthermore, many temperature-sensitive mutants in which transcription of ribosomal protein genes is temperature sensitive appear to be defective in the secretory pathway (17). As the membrane is the end product of much of the secretory pathway, these results suggest an important coupling of plasma membrane and ribosome biosynthesis. We proposed the existence of a signal transduction pathway from the plasma membrane to the nucleus. According to this model, a signal generated by the defect in de novo synthesis of membrane should be transmitted to the nucleus and cause specific and significant transcriptional repression of ribosomal genes. It was recently suggested that stress in the plasma membrane is monitored by Pkc1, which initiates a signal transduction pathway that leads to the repression (24). In order to elucidate the molecular mechanism of the signal transduction pathway, we have screened for mutants defective in the response to a secretory defect.Here we describe the isolation and molecular characterization of RRS1, encoding an essential nuclear protein of 203 amino acids. In the rrs1-1 mutant, a secretory defect fails to cause transcriptional repression of either rRNA or ribosomal protein genes. The mutant gene, rrs1-1, had a single nucleotide difference within codon 114, resulting in a stop codon. The amino acid sequence of R...
A multidrug resistance gene, YDR1, of Saccharomyces cerevisiae, which encodes a 170-kDa protein of a member of the ABC superfamily, was identified. Disruption of YDR1 resulted in hypersensitivity to cycloheximide, cerulenin, compactin, staurosporine and fluphenazine, indicating that YDR1 is an important determinant of cross resistance to apparently-unrelated drugs. The Ydr1 protein bears the highest similarity to the S. cerevisiae Snq2 protein required for resistance to the mutagen 4-NQO. The drug-specificity analysis of YDR1 and SNQ2 by gene disruption, and its phenotypic suppression by the overexpressed genes, revealed overlapping, yet distinct, specificities. YDR1 was responsible for cycloheximide, cerulenin and compactin resistance, whereas, SNQ2 was responsible for 4-NQO resistance. The two genes had overlapping specificities toward staurosporine and fluphenazine. The transcription of YDR1 and SNQ2 was induced by various drugs, both relevant and irrelevant to the resistance caused by the gene, suggesting that drug specificity can be mainly attributed to the functional difference of the putative transporters. The transcription of these genes was also increased by heat shock. The yeast drug-resistance system provides a novel model for mammalian multidrug resistance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.