Phospholipases in yeast

The central role that different phospholipases play in many signal transduction pathways has been intensively studied by classical biochemical and molecular approaches. One approach not extensively pursued, has been the use of yeast as a model system for functional analysis of different aspects of phospholipase signalling. This review concentrates on attempts to establish yeast in this role and aims to demonstrate the potential offered by this approach.     

Medicinal yeast extracts

Alcoholic extracts of bakers' yeast (Saccharomyces cerevisiae) have been used for over 60 years in over-the-counter medications for the treatment of hemorrhoids, burns, and wounds. Although previous studies suggested that small peptides were responsible for the medical observations, the peptides were never resolved into separate fractions and identified. In the present report, a protein fraction was prepared by RPC18 chromatography of the extract which enhances wound closure in both diabetic and non-diabetic littermates. The peptides are active in nanomolar amounts and are 600 times more active than the initial extract. SDS-PAGE and N-terminal amino acid sequencing identified 4 polypeptides in the extract. Three of the proteins were small molecular weight stress-associated proteins: copper, zinc superoxide-dismutase, ubiquitin, and glucose lipid regulated protein (HSP 12). The fourth protein, acyl-CoA binding protein II, has not been previously associated with stress proteins.     

Functional interaction of yeast elongation factor 3 with yeast ribosomes

Elongation factor 3 (EF-3) is a unique and essential requirement of the fungal translational apparatus. EF-3 is a monomeric protein with a molecular mass of 116,000. EF-3 is required by yeast ribosomes for in vitro translation and for in vivo growth. The protein stimulates the binding of EF-1 alpha :GTP:aa-tRNA ternary complex to the ribosomal A-site by facilitating release of deacylated-tRNA from the E-site. The reaction requires ATP hydrolysis. EF-3 contains two ATP-binding sequence motifs (NBS). NBSI is sufficient for the intrinsic ATPase function. NBSII is essential for ribosome-stimulated activity. By limited proteolysis, EF-3 was divided into two distinct functional domains. The N-terminal domain lacking the highly charged lysine blocks failed to bind ribosomes and was inactive in the ribosome-stimulated ATPase activity. The C-terminally derived lysine-rich fragment showed strong binding to yeast ribosomes. The purported S5 homology region of EF-3 at the N-terminal end has been reported to interact with 18S ribosomal RNA. We postulate that EF-3 contacts rRNA and/or protein(s) through the C-terminal end. Removal of these residues severely weakens its interaction mediated possibly through the N-terminal domain of the protein.     

酵母细胞凋亡研究进展

细胞凋亡是调节生物体正常发育和生命活动的一种不可缺少的机制,其研究生命力在于最终能够有利于疾病机制的阐明以及新疗法的探索及问世。酵母细胞由于凋亡过程的高度保守性及其作为分子生物学模式物种的先天优势,近年来一直是凋亡研究的热点。目前对酵母细胞凋亡的核心分子、传导通路和诱因等已经有了深入的了解。     

Riboneogenesis in yeast

Glucose is catabolized in yeast via two fundamental routes, glycolysis and the oxidative pentose phosphate pathway, which produces NADPH and the essential nucleotide component ribose-5-phosphate. Here, we describe riboneogenesis, a thermodynamically driven pathway that converts glycolytic intermediates into ribose-5-phosphate without production of NADPH. Riboneogenesis begins with synthesis, by the combined action of transketolase and aldolase, of the seven-carbon bisphosphorylated sugar sedoheptulose-1,7-bisphosphate. In the pathway's committed step, sedoheptulose bisphosphate is hydrolyzed to sedoheptulose-7-phosphate by the enzyme sedoheptulose-1,7-bisphosphatase (SHB17), whose activity we identified based on metabolomic analysis of the corresponding knockout strain. The crystal structure of Shb17 in complex with sedoheptulose-1,7-bisphosphate reveals that the substrate binds in the closed furan form in the active site. Sedoheptulose-7-phosphate is ultimately converted by known enzymes of the nonoxidative pentose phosphate pathway to ribose-5-phosphate. Flux through SHB17 increases when ribose demand is high relative to demand for NADPH, including during ribosome biogenesis in metabolically synchronized yeast cells.     

Making magnetic yeast

This study demonstrates that normal yeast cells can be magnetized, and identifies local redox control via carbon metabolism and iron supply as key factors involved in magnetization.     

Necrosis in yeast

Necrosis was long regarded as an accidental cell death process resulting from overwhelming cellular injury such as chemical or physical disruption of the plasma membrane. Such a definition, however, proved to be inapplicable to many necrotic scenarios. The discovery that genetic manipulation of several proteins either protected or enhanced necrotic cell death argued in favor of a regulated and hence programmed process, as it is the case for apoptosis. For more than a decade, yeast has served as a model for apoptosis research; recently, evidence accumulated that it also harbors a necrotic program. Here, we summarize the current knowledge about factors that control necrotic cell death in yeast. Mitochondria, aging and a low pH are positive regulators of this process while cellular polyamines (e.g. spermidine) and endonuclease G as well as homeostatic organelles like the vacuole or peroxisomes are potent inhibitors of necrosis. Physiological necrosis may stimulate intercellular signaling via the release of necrotic factors that promote viability of healthy cells and, thus, assure survival of the clone. Together, the data obtained in yeast argue for the existence of a necrotic program, which controls longevity and whose physiological function may thus be aging.     

Antisuppressors in yeast

Summary 1. Twenty-three mutations, mapping at eight different loci, were shown to prevent detectable suppression of ade2-1 and can1-100 by the ochre suppressor, ocSUPQ2. 2. Some reduce the efficiency of suppression of his5-2 and lys1-1 also. 3. Mutants from each of the eight loci prevented the lethal phenotype of ocSUPQ2 in [psi+] strains. They are, therefore, antisuppressor mutations. 4. One of the loci, asu3, is centromere-linked; two of the loci, asu2 and asu6, are linked to each other.