An efficient technique for the isolation of yeast spores and the preparation of spheroplast lysates active in protein synthesis

Rapid identification of reproductive toxicants among environmental chemicals using an in vivo evaluation of gametogenesis in budding yeast Saccharomyces cerevisiae

Infertility affects ∼12 % of couples, with environmental chemical exposure as a potential contributor. Of the chemicals that are actively manufactured, very few are assessed for reproductive health effects. Rodents are commonly used to evaluate reproductive effects, which is both costly and time consuming. Thus, there is a pressing need for rapid methods to test a broader range of chemicals. Here, we developed a strategy to evaluate large numbers of chemicals for reproductive toxicity via a yeast, S. cerevisiae high-throughput assay to assess gametogenesis as a potential new approach method (NAM). By simultaneously assessing chemicals for growth effects, we can distinguish if a chemical affects gametogenesis only, proliferative growth only or both. We identified a well-known mammalian reproductive toxicant, bisphenol A (BPA) and ranked 19 BPA analogs for reproductive harm. By testing mixtures of BPA and its analogs, we found that BPE and 17 β-estradiol each together with BPA showed synergistic effects that worsened reproductive outcome. We examined an additional 179 environmental chemicals including phthalates, pesticides, quaternary ammonium compounds and per- and polyfluoroalkyl substances and found 57 with reproductive effects. Many of the chemicals were found to be strong reproductive toxicants that have yet to be tested in mammals. Chemicals having affect before meiosis I division vs. meiosis II division were identified for 16 gametogenesis-specific chemicals. Finally, we demonstrate that in general yeast reproductive toxicity correlates well with published reproductive toxicity in mammals illustrating the promise of this NAM to quickly assess chemicals to prioritize the evaluation for human reproductive harm.

Trehalases from spores and vegetative cells of yeast Saccharomyces cerevisiae

Trehalase (THA) activity from S. cerevisiae spores and vegetative cells could be differentiated in cell-free extracts. THA from the vegetative cells has an optimal activity at neutral pH whereas biphase pH optimum in the spores was observed. The enzyme from the spores exhibited higher thermostability than that from the vegetative cells. The presence of magnesium ions was necessary mainly for THA activity from the vegetative cells. The effect of the other metal ions studied: Hg2+, Ag2+, Cu2+, Fe3+, Ni2+, Cd2+ etc. (Table II), on THA from both sources was almost the same, however, the spores THA was resistant to Pb2+ and especially to Zn2+. Moreover, the influence of inorganic polyphosphates and polyamines was also quite dissimilar. Polyphosphates inhibited THA from the vegetative cells and to a smaller extent from the spores. On the other hand, polyamines stimulated highly THA activity from vegetative yeast cells in contrast to spores one. The effect of these ions modulators would facilitate differentiating of THA activity in the cell-free extracts from both sources. These data could be interpreted as phenotypic reflections of trehalase genes expression in the S. cerevisiae cells.

Expression and function of the trehalase genes NTH1 and YBR0106 in Saccharomyces cerevisiae

The biological function of the trehalose-degrading yeast enzyme neutral trehalase consists of the control of the concentration of trehalose, which is assumed to play a role in thermotolerance, in germination of spores, and in other life functions of yeast. Resequencing of the neutral trehalase gene NTH1 on chromosome IV resulted in the observation of two possible start codons (Kopp, M., Nwaka, S., and Holzer, H. (1994) Gene (Amst.) 150, 403-404). We show here that only the most upstream start codon which initiates translation of the longest possible ORF is used for expression of NTH1 in vivo. A gene with 77% identity with NTH1, YBR0106, which was discovered during sequencing of chromosome II (Wolfe, K. H., and Lohan, A. J. E. (1994) Yeast 10, S41-S46), is shown here to be expressed into mRNA. Experiments with a mutant disrupted in the YBR0106 ORF showed, in contrast to a NTH1 deletion mutant, no changes in trehalase activity and in trehalose concentration. However, similar to the NTH1 gene a requirement of the intact YBR0106 gene for thermotolerance is demonstrated in experiments with the respective mutants. This indicates that the products of the likely duplicated YBR0106 gene and the NTH1 gene serve a heat shock protein function. In case of the YBR0106 gene, this is the only phenotypic feature found at present.

Specific protein kinase from Saccharomyces cerevisiae cells phosphorylating 60S ribosomal proteins

A protein kinase, specific for 60S ribosomal proteins, has been isolated from Saccharomyces cerevisiae cells, purified to almost homogeneity and characterized. The isolated enzyme is not related to other known protein kinases. Enzyme purification comprised three chromatography steps; DEAE-cellulose, phosphocellulose and heparin-Sepharose. SDS/PAGE analysis of the purified enzyme, indicated a molecular mass of around 71 kDa for the stained single protein band. The specific activity of the protein kinase was directed towards the 60S ribosomal proteins L44, L44', L45 and a 38 kDa protein. All the proteins are phosphorylated only at the serine residues. None of the 40S ribosomal proteins were phosphorylated in the presence of the kinase. For that reason we have named the enzyme the 60S kinase. An analysis of the phosphopeptide maps of acidic ribosomal proteins, phosphorylated at either the 60S kinase or casein kinase II, showed almost identical patterns. Using the immunoblotting technique, the presence of the kinase has been detected in extracts obtained from intensively growing cells. These findings suggest an important role played by the 60S kinase in the regulation of ribosomal activity during protein synthesis.

Properties of the major antigens of rat and human Pneumocystis carinii

The major rat and human Pneumocystis carinii antigens were analyzed for their susceptibility to treatment with enzymes and other procedures by immunoblotting, immunofluorescence, and light microscopy. Carbohydrate residues were further analyzed by lectin-binding experiments. The 116-kilodalton (kDa) band of rat P. carinii was susceptible to proteolytic (e.g., trypsin) and glycolytic (e.g., Zymolyase) treatments but not to a variety of other procedures (e.g., lipase). This moiety reacted strongly with concanavalin A and wheat germ agglutinin, indicating the presence of mannosyl or glucosyl and N-acetylglucosamine residues. Immunofluorescence staining and surface labeling suggested that the 116-kDa antigen was located on the P. carinii cell wall. The 45- and 50-kDa bands were as sensitive as the 116-kDa band to degradative treatments when studied after immobilization onto nitrocellulose but were more resistant to proteolytic enzymes when studied in situ on whole organisms. These moieties exhibited poor binding to lectins and reactivity by surface-labeling procedures. The 116-kDa band of human P. carinii appeared to be a glycoprotein with characteristics similar to those of its counterpart in rats, whereas the human P. carinii 40-kDa band exhibited protein and carbohydrate properties more closely related to those of the 45- and 50-kDa rat-derived antigens. We conclude that P. carinii antigens are complex glycoproteins and that this information will be helpful in developing strategies for their isolation and purification and study of their function.

A method for isolation of RNA from Pneumocystis carinii

Total RNA from Pneumocystis carinii obtained directly from the rat lung and from short term culture on A549 cells was evaluated for size and purity. An isolation procedure using guanidine isothiocyanate and lithium chloride was preferable to a hot phenol method. Host cells were eliminated by hypotonic lysis and a series of microfiltrations. Pneumocystis carinii were pretreated with Zymolyase for increased susceptibility to chaotropic agents. The major ribosomal species of P. carinii RNA migrated similarly to Saccharomyces cerevisiae rRNA. The 28s-like species migrated well ahead of rat and A549 cell rRNA and well behind the prokaryotic large rRNA species.

Substrate-inhibitor cooperative interactions with microbial dihydrofolate reductases

Cooperativity in the binding of two substrates to an enzyme is a now well-established phenomenon. The x-ray crystallographic structure of the E. coli DHFR binary TMP complex compared with the ternary enzyme-NADPH-TMP complex suggests without too imaginative extrapolation, that the conformational changes resulting from the binding of one ligand aid in favorably positioning potential binding sites for the second ligand. Of greater importance is the fact that the extent to which inhibitor binding is enhanced by the binding of NADPH varies from species to species. To a significant extent, for example, the selectivity of TMP is enhanced by the increase in its binding to the E. coli enzyme when NADPH is present as compared with several mammalian enzymes. The reverse, negative cooperativity (a decrease in binding of a substance when moving from the binary to a ternary complex), is perhaps less common and certainly less well studied. The present paper deals with one such enzyme, the DHFR from C. albicans, and by reference to another, that from S. cerevisiae, where it is shown that the binding of substrates exhibit strong negative cooperativity. It was of interest also to determine the relationship between inhibitor/NADPH cooperativity and the relative insensitivity of N. gonorrhoeae to TMP. Equilibrium studies show that the binding of TMP in binary complex with this enzyme is exceedingly poor and that a 2,200-fold cooperative effect brings the gonococcal enzyme Ki within one order of magnitude of the E. coli enzyme Ki. Even so, it takes synergism of another sort (with sulfamethoxazole) and high doses to make co-trimoxazole therapy feasible for treating gonorrhoeae. The comparative results on the gonococcal enzyme for a family of near relatives of TMP are of interest also for the reason that the structure-activity relationships with this enzyme are quite different from those of the E. coli and other microbial enzymes. Finally, it should be pointed out that although the negative cooperativity found for the candida and saccharomyces enzymes is relatively large, it is the values of the substrate Michaelis constants that are physiologically relevant. The Km values of the yeast enzymes are within the range for other DHFR and therefore the intracellular activity of the enzymes should not be compromised.

A cytoplasmic, cyclic nucleotide-independent casein kinase II from Saccharomyces cerevisiae

Two molecular forms of casein kinase II (an ATP: protein phosphotransferase, EC 2.7.1.37) from yeast were isolated and characterized. The first form was composed of three polypeptide subunits with molecular weights of 41000, 37000 and 24000. The second form contained two larger polypeptides and lacked an autophosphorylatable 24 kDa subunit. The properties of both enzyme forms were found to be practically the same in respect to the substrate and phosphate donor specificities, kinetics, their sensitivity to heparin, etc. The results obtained strongly indicate that isolated yeast casein kinase II does not necessarily require the smallest subunit for the enzyme activity.