酵母朊病毒的遗传与增殖

１９８２年,Ｐｒｕｓｉｎｅｒ等发现,在感染瘙痒病的仓鼠脑中有一种异常蛋白,名其为“蛋白质感染颗粒”（ｐｒｏｔｅｉｎａｃｅｏｕｓｉｎｆｅｃｔｉｏｕｓｐａｒｔｉ－ｃｌｅ）。Ｐｒｕｓｉｎｅｒ用ｐｒｉｏｎ（现译为朊病毒）这一名词把这类病原体与病毒、细菌、真菌以及其它已知的病原体区分开。后来发现这种蛋白质能够自我催化复制,且有两种构象,即正常态的ＰｒＰＣ和感染态的ＰｒＰＳＣ。两者的化学性质也不同：ＰｒＰＣ能溶于非变性洗涤剂而ＰｒＰＳＣ不溶;ＰｒＰＣ易被蛋白酶消化而ＰｒＰＳＣ则具部分抗性。在酵母中,朊病毒不…     

Regulation,Cell Differentiation and Protein-Based Inheritance

Recent research using fungi as models provide new insight into the ability of regulatory networks to generate cellular states that are sufficiently stable to be faithfully transmitted to daughter cells, thereby generating epigenetic inheritance. Such protein-based inheritance is driven by infectious factors endowed with properties usually displayed by prions. We emphasize the contribution of regulatory networks to the emerging properties displayed by cells.     

Prions: an evolutionary perspective.

Studies in both prion-due diseases in mammals and some non-Mendelian hereditary processes in yeasts have demonstrated that certain proteins are able to transmit structural information and self-replication. This induces the corresponding conformational changes in other proteins with identical or similar sequences. This ability of proteins may have been very useful during prebiotic chemical evolution, prior to the establishment of the genetic code. During this stage, proteins (proteinoids) must have molded and selected their structural folding units through direct interaction with the environment. The proteinoids that acquired the ability to propagate their conformations (which we refer to as conformons) would have acted as reservoirs and transmitters of a given structural information and hence could have acted as selectors for conformational changes. Despite the great advantage that arose from the establishment of the genetic code, the ability to propagate conformational changes did not necessarily disappear. Depending on the degree of involvement of this capacity in biological evolution, we propose two not mutually exclusive hypotheses: (i) extant prions could be an atavism of ancestral conformons, which would have co-evolved with cells, and (ii) the evolution of conformons would have produced cellular proteins, able to transmit structural information, and, in some cases, participating in certain processes of regulation and epigenesis. Therefore, prions could also be seen as conformons of a conventional infectious agent (or one that co-evolved with it independently) that, after a longer or shorter adaptive period, would have interacted with conformons from the host cells.     

Saccharomyces vafer andS. inconspicuus spp.n.

During the re-examination of cultures deposited with the Yeast Division of the Centraalbureau voor Schimmelcultures, Delft, representatives of two hitherto undescribed species of the genusSaccharomyces were encountered.     

More than Just a Phase: Prions at the Crossroads of Epigenetic Inheritance and Evolutionary Change

A central tenet of molecular biology is that heritable information is stored in nucleic acids. However, this paradigm has been overturned by a group of proteins called “prions.” Prion proteins, many of which are intrinsically disordered, can adopt multiple conformations, at least one of which has the capacity to self-template. This unusual folding landscape drives a form of extreme epigenetic inheritance that can be stable through both mitotic and meiotic cell divisions. Although the first prion discovered—mammalian PrP—is the causative agent of debilitating neuropathies, many additional prions have now been identified that are not obviously detrimental and can even be adaptive. Intrinsically disordered regions, which endow proteins with the bulk property of “phase-separation,” can also be drivers of prion formation. Indeed, many protein domains that promote phase separation have been described as prion-like. In this review, we describe how prions lie at the crossroads of phase separation, epigenetic inheritance, and evolutionary adaptation.     

Susceptibility of Saccharomyces spp. and Schwanniomyces spp. to the aminoglycoside antibiotic G418.

Industrially useful polyploid yeasts such as the brewing yeasts do not possess any auxotrophic genetic markers and hence are not easily amenable to plasmid-mediated DNA transformations. In an attempt to obtain genetic markers, a number of useful Saccharomyces sp. strains and some amylolytic Schwanniomyces sp. strains were tested for their susceptibility to the antibiotic Geneticin G418 , a 2-deoxystreptamine reported to be active against bacteria, yeasts, and plant and animal cells. All of the Saccharomyces sp. strains, including the brewing strains, were found to be susceptible to G418 in the concentration range of 150 to 500 micrograms/ml. Of the three Schwanniomyces species investigated, only Schwanniomyces castellii (strain 1402) was found to be resistant to G418 at concentrations up to 1 mg/ml. Resistance was exhibited both in liquid media and on glycerol-peptone-yeast extract agar plates. This finding is interesting in view of the possibility of using this strain as a DNA donor for transformations aimed at introducing the amylolytic capability into brewing yeasts.     

Impact of ROS on ageing of two fungal model systems: Saccharomyces cerevisiae and Podospora anserina

To provide a foundation for the development of effective interventions to counteract various age-related diseases in humans, ageing processes have been extensively studied in various model organisms and systems. However, the mechanisms underlying ageing are still not unravelled in detail in any system including rather simple organisms. In this article, we review some of the molecular mechanisms that were found to affect ageing in two fungal models, the unicellular ascomycete Saccharomyces cerevisiae and the filamentous ascomycete Podospora anserina. A selection of issues like retrograde response, genomic instability, caloric restriction, mtDNA reorganisation and apoptosis is presented and discussed with special emphasis on the role reactive oxygen species (ROS) play in these diverse molecular pathways.     

Impact of ROS on ageing of two fungal model systems: Saccharomyces cerevisiae and Podospora anserina

To provide a foundation for the development of effective interventions to counteract various age-related diseases in humans, ageing processes have been extensively studied in various model organisms and systems. However, the mechanisms underlying ageing are still not unravelled in detail in any system including rather simple organisms. In this article, we review some of the molecular mechanisms that were found to affect ageing in two fungal models, the unicellular ascomycete Saccharomyces cerevisiae and the filamentous ascomycete Podospora anserina. A selection of issues like retrograde response, genomic instability, caloric restriction, mtDNA reorganisation and apoptosis is presented and discussed with special emphasis on the role reactive oxygen species (ROS) play in these diverse molecular pathways.     

Two-step fermentation of acidic grape musts: Interactions between Schizosaccharomyces pombe and Saccharomyces spp.

The interactions between Schizosaccharomyces pombe and Saccharomyces spp. (S. cerevisiae, S. cerevisiae sake, S. bayanus, S. uvarum) were investigated by growing the yeasts in sterile, partially fermented glucose asparagine medium in flasks, and also in the Ecologen containing either synthetic medium or grape must be separating the adjacent chambers with membranes which allow free movement of medium but not of cells. The growth of Sch. pombe was inhibited by Saccharomyces spp. to a varied extent, but the reverse was not observed. Saccharomyces uvarum, and S. cerevisiae more strongly inhibited Sch. pombe than the other species tested. All three strains of Sch. pombe (ICV-M, BG, ATCC-16979) were inhibited by S. cerevisiae although ICV-M and ATCC strains were more sensitive than BG. The higher growth rate of S. cerevisiae resulted in the exhaustion of nutrients, and its metabolic products could possibly be responsible for the growth inhibition of Sch. pombe. In the light of the present experimental results, the suitability of a two-step fermentation process for making better quality wines from acidic grape musts is discussed.     

Prions and manganese: A maddening beast

The prion protein is well known because of its association with prion diseases. These diseases, which include variant CJD, are unusual because they are neurodegenerative diseases that can be transferred between individuals experimentally. The prion protein is also widely known as a copper binding protein. The binding of copper to the prion protein is possibly necessary for its normal cellular function. The prion protein has also been suggested to bind other metals, and among these, manganese. Despite over ten years of research on manganese and prion disease, this interaction has often been dismissed or at best seen as a poor cousin to the involvement of copper. However, recent data has shown that manganese could stabilise prions in the environment and that chelation therapy specifically aimed at manganese can extend the life of animals with prion disease. This article reviews the evidence for a link between prions and manganese.     

Prions: health scare and biological challenge

Although human prion diseases are rare, the incidence of 'new variant' Creutzfeldt-Jakob disease in the United Kingdom is increasing exponentially. Given that this disease is probably the result of infection with bovine prions, understanding how prions replicate--and how to counteract their action--has become a central issue for public health. What are the links between the bovine and human prion diseases, and how do prions reach and damage the central nervous system?     

Phenotypic expression of Kluyveromyces lactis killer toxin against Saccharomyces spp.

The secretion of killer toxins by some strains of yeasts is a phenomenon of significant industrial importance. The activity of a recently discovered Kluyveromyces lactis killer strain against a sensitive Saccharomyces cerevisiae strain was determined on peptone-yeast extract-nutrient agar plates containing as the carbon source glucose, fructose, galactose, maltose, or glycerol at pH 4.5 or 6.5. Enhanced activity (50 to 90% increase) was found at pH 6.5, particularly on the plates containing galactose, maltose, or glycerol, although production of the toxin in liquid medium was not significantly different with either glucose or galactose as the carbon source. Results indicated that the action of the K. lactis toxin was not mediated by catabolite repression in the sensitive strain. Sensitivities of different haploid and polyploid Saccharomyces yeasts to the two different killer yeasts S. cerevisiae (RNA-plasmid-coded toxin) and K. lactis (DNA-plasmid-coded toxin) were tested. Three industrial polyploid yeasts sensitive to the S. cerevisiae killer yeast were resistant to the K. lactis killer yeast. The S. cerevisiae killer strain itself, however, was sensitive to the K. lactis killer yeast.     

Transport and Retention Mechanisms Govern Lipid Droplet Inheritance in Saccharomyces cerevisiae

Lipid droplets are ubiquitous cellular structures involved in energy homeostasis and metabolism that have long been considered as simple inert deposits of lipid. Here, we show that lipid droplets are bona fide organelles that are actively partitioned between mother cell and daughter cell in Saccharomyces cerevisiae. Video microscopy revealed that a subset of lipid droplets moves from mother cell to bud in an ordered, vectorial process, while the remaining lipid droplets are retained by the mother cell. Bud‐directed movement of lipid droplets is mediated by the molecular motor Myo2p, while retention of lipid droplets occurs at the perinuclear endoplasmic reticulum. Lipid droplets are thus apportioned between mother cell and daughter cell at cell division rather than being made anew.      

Prions: Generation and Spread Versus Neurotoxicity

Neurodegenerative diseases are characterized by the aggregation of misfolded proteins in the brain. Among these disorders are the prion diseases, which are transmissible, and in which the misfolded proteins (“prions”) are also the infectious agent. Increasingly, it appears that misfolded proteins in Alzheimer and Parkinson diseases and the tauopathies also propagate in a “prion-like” manner. However, the association between prion formation, spread, and neurotoxicity is not clear. Recently, we showed that in prion disease, protein misfolding leads to neurodegeneration through dysregulation of generic proteostatic mechanisms, specifically, the unfolded protein response. Genetic and pharmacological manipulation of the unfolded protein response was neuroprotective despite continuing prion replication, hence dissociating this from neurotoxicity. The data have clear implications for treatment across the spectrum of these disorders, targeting pathogenic processes downstream of protein misfolding.     

Influence of the membrane on T-2 toxin toxicity in Saccharomyces spp.

In growing cells of Saccharomyces cerevisiae and Saccharomyces carlsbergensis, T-2 toxin inhibits cell growth. We have examined the role of the yeast membranes in the uptake mechanism(s) of T-2 toxin. The effects of membrane-modulating agents, ethanol, cetyltrimethylammonium bromide, Triton X-100, and heat were studied; these agents were found to increase the sensitivity of the yeasts toward T-2 toxin. In the presence of 5% (vol/vol) ethanol, 2 micrograms of T-2 toxin per ml caused complete inhibition of growth. In the presence of 1 microgram of cetyltrimethylammonium bromide per ml, yeast cells became sensitive to T-2 toxin, starting with a concentration of 0.5 micrograms/ml. Triton X-100 at concentrations below 1% (vol/vol) sensitized the cells toward T-2 toxin, but at higher concentrations it protected the cells from T-2 toxin. Temperatures of incubation between 7 and 30 degrees C influenced the growth reduction caused by T-2 toxin. The greatest observed reduction of growth in T-2 toxin-treated cultures occurred at 30 degrees C. To further prove that the membrane influences the interaction of T-2 toxin with yeasts, we have studied a yeast mutant with a reduced plasma membrane permeability (G. H. Rank et al., Mol. Gen. Genet. 152:13-18, 1977). This yeast mutant proved to be resistant to T-2 toxin concentrations of up to 50 micrograms/ml. These results show that the membrane plays a significant role in the interaction of T-2 toxin with yeast cells.     

Prions and serpins: structural analogs and their consequences. I. Protease-transport hypothesis

The structural analogy between prions pathogenic form and serine proteinase inhibitors (serpins) was laid into the basis of explaining the prion diseases main peculiarities--nucleic-acid-free transfer of infection, neurodegenerative processes, existence of the minimal infective dose, long-term latent period and some others. The assumption about pathogenic prions as the proteins supplying the extracellular proteinases transport into the intracellular space permits to bring the pathogenesis of prion diseases to the known and partially proved processes order regarding the case of prion diseases.