Mitochondrial inheritance in budding yeast

During the past decade significant advances were made toward understanding the mechanism of mitochondrial inheritance in the yeast Saccharomyces cerevisiae . A combination of genetics, cell-free assays and microscopy has led to the discovery of a great number of components. These fall into three major categories: cytoskeletal elements, mitochondrial membrane components and regulatory proteins. These proteins mediate activities, including movement of mitochondria from mother cells to buds, segregation of mitochondria and mitochondrial DNA, and equal distribution of the organelle between mother cells and buds during yeast cell division.     

Clathrin-mediated endocytosis in budding yeast

Clathrin-mediated endocytosis in the budding yeast Saccharomyces cerevisiae involves the ordered recruitment, activity and disassembly of nearly 60 proteins at distinct sites on the plasma membrane. Two-color live-cell fluorescence microscopy has proven to be invaluable for in vivo analysis of endocytic proteins: identifying new components, determining the order of protein arrival and dissociation, and revealing even very subtle mutant phenotypes. Yeast genetics and functional genomics facilitate identification of complex interaction networks between endocytic proteins and their regulators. Quantitative datasets produced by these various analyses have made theoretical modeling possible. Here, we discuss recent findings on budding yeast endocytosis that have advanced our knowledge of how -60 endocytic proteins are recruited, perform their functions, are regulated by lipid and protein modifications, and are disassembled, all with remarkable regularity.     

Single-cell phenomics in budding yeast

The demand for phenomics, a high-dimensional and high-throughput phenotyping method, has been increasing in many fields of biology. The budding yeast Saccharomyces cerevisiae, a unicellular model organism, provides an invaluable system for dissecting complex cellular processes using high-resolution phenotyping. Moreover, the addition of spatial and temporal attributes to subcellular structures based on microscopic images has rendered this cell phenotyping system more reliable and amenable to analysis. A well-designed experiment followed by appropriate multivariate analysis can yield a wealth of biological knowledge. Here we review recent advances in cell imaging and illustrate their broad applicability to eukaryotic cells by showing how these techniques have advanced our understanding of budding yeast.     

Vacuolar dynamics in synchronously budding yeast

Summary A simple and rapid method for obtaining synchronously budding cultures of Saccharomyces cerevisiae is described. Synchronous cultures were started with homogeneous cell fractions isolated from exponentially growing cultures by isopycnic centrifugation in osmotically inactive media. The technique of fractionation is based on changes of cell density throughout the budding cycle. These changes are correlated with vacuolar changes observed in the light and electron microscope. During bud initiation the large vacuoles in late budding cells shrink and fragment into small vacuoles. Simultaneously the density of the cells increases. Later stages of the budding cycle are characterized by the distribution of the small vacuoles between mother and daughter cell, followed by their fusion and expansion, and by a decreasing density of the cells. The relative changes in cell density and dry weight and in the content of different macromolecules during the budding cycle suggest a cyclic change between utilization of endogenous and exogenous substrates. This is discussed in terms of a cyclic consumption and accumulation of vacuolar pools.     

Predicting protein localization in budding yeast

MOTIVATION: Most of the existing methods in predicting protein subcellular location were used to deal with the cases limited within the scope from two to five localizations, and only a few of them can be effectively extended to cover the cases of 12-14 localizations. This is because the more the locations involved are, the poorer the success rate would be. Besides, some proteins may occur in several different subcellular locations, i.e. bear the feature of 'multiplex locations'. So far there is no method that can be used to effectively treat the difficult multiplex location problem. The present study was initiated in an attempt to address (1) how to efficiently identify the localization of a query protein among many possible subcellular locations, and (2) how to deal with the case of multiplex locations. RESULTS: By hybridizing gene ontology, functional domain and pseudo amino acid composition approaches, a new method has been developed that can be used to predict subcellular localization of proteins with multiplex location feature. A global analysis of the proteins in budding yeast classified into 22 locations was performed by jack-knife cross-validation with the new method. The overall success identification rate thus obtained is 70%. In contrast to this, the corresponding rates obtained by some other existing methods were only 13-14%, indicating that the new method is very powerful and promising. Furthermore, predictions were made for the four proteins whose localizations could not be determined by experiments, as well as for the 236 proteins whose localizations in budding yeast were ambiguous according to experimental observations. However, according to our predicted results, many of these 'ambiguous proteins' were found to have the same score and ranking for several different subcellular locations, implying that they may simultaneously exist, or move around, in these locations. This finding is intriguing because it reflects the dynamic feature of these proteins in a cell that may be associated with some special biological functions.     

The spindle cycle in budding yeast

The mitotic spindle of the budding yeast Saccharomyces cerevisiae will probably be the first such organelle to be understood in molecular detail. Here we describe the mitotic spindle cycle of budding yeast using electron-microscope-derived structures and dynamic live-cell imaging. Recent work has revealed that many general aspects of mitosis are conserved, making budding yeast an excellent model for the study of mitosis.     

Cell cycle-regulated promoters in budding yeast

Cell cycle-regulated promoters are activated in response to specific cues in the cell cycle. By studying the mechanism of their transient activation, we may identify the molecules that trigger progress through the cell cycle.     

ERAD substrate recognition in budding yeast

During protein synthesis, the orderly progression of folding, modification, and assembly is paramount to function and vis-à-vis cellular viability. Accordingly, sophisticated quality control mechanisms have evolved to monitor protein maturation throughout the cell. Proteins failing at any step are segregated and degraded as a preventative measure against potential toxicity. Although protein quality control is generally poorly understood, recent research advances in endoplasmic reticulum-associated degradation (ERAD) pathways have provided the most detailed view so far. The discovery of distinct substrate processing sites established a biochemical basis for genetic profiles of model misfolded proteins. Detailed mechanisms for substrate recognition were recently uncovered. For some proteins, sequential glycan trimming steps set a time window for folding. Proteins still unfolded at the final stage expose a specific degradation signal recognized by the ERAD machinery. Through this mechanism, the system does not in fact know that a molecule is “misfolded”. Instead, it goes by the premise that proteins past due have veered off their normal folding pathways and therefore aberrant.     

Nutrient-regulated protein kinases in budding yeast

The ability of cells to react appropriately to nutritional cues is of fundamental importance, and in budding yeast, a small number of intracellular protein kinases, PKA, Snf1p/AMP-activated kinase, TOR, Gcn2p, and the cyclin-dependent kinase Pho85p have key roles. A recently characterized enzyme, PAS kinase, may be a new member of this group of nutritional transducers.     

酵母菌与其“芽体”

从细胞生物学和分子生物学的层面对酵母菌的芽体形成过程及芽体与母体细胞的相关性作了综合评述。     

The centromere of budding yeast

Stable maintenance of genetic information during meiosis and mitosis is dependent on accurate chromosome transmission. The centromere is a key component of the segregational machinery that couples chromosomes with the spindle apparatus. Most of what is known about the structure and function of the centromeres has been derived from studies on yeast cells. In Saccharomyces cerevisiae, the centromere DNA requirements for mitotic centromere function have been defined and some of the proteins required for an active complex have been identified. Centromere DNA and the centromere proteins form a complex that has been studied extensively at the chromatin level. Finally, recent findings suggest that assembly and activation of the centromere are integrated in tethe cell cycle.     

Sociobiology of the budding yeast

Social theory has provided a useful framework for research with microorganisms. Here I describe the advantages and possible risks of using a well-known model organism, the unicellular yeast Saccharomyces cerevisiae, for sociobiological research. I discuss the problems connected with clear classification of yeast behaviour based on the fitness-based Hamilton paradigm. Relevant traits include different types of communities, production of flocculins, invertase and toxins, and the presence of apoptosis.     

Sporulation in the budding yeast Saccharomyces cerevisiae

In response to nitrogen starvation in the presence of a poor carbon source, diploid cells of the yeast Saccharomyces cerevisiae undergo meiosis and package the haploid nuclei produced in meiosis into spores. The formation of spores requires an unusual cell division event in which daughter cells are formed within the cytoplasm of the mother cell. This process involves the de novo generation of two different cellular structures: novel membrane compartments within the cell cytoplasm that give rise to the spore plasma membrane and an extensive spore wall that protects the spore from environmental insults. This article summarizes what is known about the molecular mechanisms controlling spore assembly with particular attention to how constitutive cellular functions are modified to create novel behaviors during this developmental process. Key regulatory points on the sporulation pathway are also discussed as well as the possible role of sporulation in the natural ecology of S. cerevisiae.     

Cell polarization and cytokinesis in budding yeast

Asymmetric cell division, which includes cell polarization and cytokinesis, is essential for generating cell diversity during development. The budding yeast Saccharomyces cerevisiae reproduces by asymmetric cell division, and has thus served as an attractive model for unraveling the general principles of eukaryotic cell polarization and cytokinesis. Polarity development requires G-protein signaling, cytoskeletal polarization, and exocytosis, whereas cytokinesis requires concerted actions of a contractile actomyosin ring and targeted membrane deposition. In this chapter, we discuss the mechanics and spatial control of polarity development and cytokinesis, emphasizing the key concepts, mechanisms, and emerging questions in the field.     

Development of cell polarity in budding yeast

The development of cell polarity involves virtually every aspect of cell biology. Yeast are less complex than cells traditionally used for studies on cell polarity and are amendable to sophisticated genetic analysis. This has resulted in a growing number of molecular markers for yeast cell polarity and an increasingly well-defined progression of molecular events required for bud formation. Together, these factors provide a favorable context in which to understand how the interplay between a large number of processes can polarize a cell. Many genes required for morphogenesis have been identified, and genetic interactions provide evidence that the products of these genes function together. Studies on cell polarity development in S. cerevisiae have demonstrated a requirement for small GTP-binding proteins and have established functional relationships between temporally coincident events. With the continued identification and analysis of genes required for morphogenesis, and the pursuit of these studies on a cytological and biochemical level, studies on yeast will continue to contribute to our understanding of cell polarity development.     

Predicting 22 protein localizations in budding yeast

According to the recent experiments, proteins in budding yeast can be distinctly classified into 22 subcellular locations. Of these proteins, some bear the multi-locational feature, i.e., occur in more than one location. However, so far all the existing methods in predicting protein subcellular location were developed to deal with only the mono-locational case where a query protein is assumed to belong to one, and only one, subcellular location. To stimulate the development of subcellular location prediction, an augmentation procedure is formulated that will enable the existing methods to tackle the multi-locational problem as well. It has been observed thru a jackknife cross-validation test that the success rate obtained by the augmented GO-FnD-PseAA algorithm [BBRC 320 (2004) 1236] is overwhelmingly higher than those by the other augmented methods. It is anticipated that the augmented GO-FunD-PseAA predictor will become a very useful tool in predicting protein subcellular localization for both basic research and practical application.     

芽殖酵母ASH1 mRNA的定位机制

mRNA定位是一种基因转录后水平的重要调控机制,对细胞的生理活动和分化发育都有着极其重要的作用。在芽殖酵母有丝分裂中,ASH1 mRNA在子细胞芽尖因不对称定位表达抑制了子细胞交配类型的转换。本综述介绍了芽殖酵母ASH1 mRNA定位的分子机制。     

Behavior of dicentric chromosomes in budding yeast

DNA double-strand breaks arise in vivo when a dicentric chromosome (two centromeres on one chromosome) goes through mitosis with the two centromeres attached to opposite spindle pole bodies. Repair of the DSBs generates phenotypic diversity due to the range of monocentric derivative chromosomes that arise. To explore whether DSBs may be differentially repaired as a function of their spatial position in the chromosome, we have examined the structure of monocentric derivative chromosomes from cells containing a suite of dicentric chromosomes in which the distance between the two centromeres ranges from 6.5 kb to 57.7 kb. Two major classes of repair products, homology-based (homologous recombination (HR) and single-strand annealing (SSA)) and end-joining (non-homologous (NHEJ) and micro-homology mediated (MMEJ)) were identified. The distribution of repair products varies as a function of distance between the two centromeres. Genetic dependencies on double strand break repair (Rad52), DNA ligase (Lif1), and S phase checkpoint (Mrc1) are indicative of distinct repair pathway choices for DNA breaks in the pericentromeric chromatin versus the arms.