Disturbance of the machinery for the gene expression by acidic pH in the repressible acid phosphatase system of Saccharomyces cerevisiae

Regulation of gene expression by ambient pH in filamentous fungi and yeasts

Life, as we know it, is water based. Exposure to hydroxonium and hydroxide ions is constant and ubiquitous, and the evolutionary pressure to respond appropriately to these ions is likely to be intense. Fungi respond to their environments by tailoring their output of activities destined for the cell surface or beyond to the ambient pH. We are beginning to glimpse how they sense ambient pH and transmit this information to the transcription factor, whose roles ensure that a suitable collection of gene products will be made. Although relatively little is known about pH signal transduction itself, its consequences for the cognate transcription factor are much clearer. Intriguingly, homologues of components of this system mediating the regulation of fungal gene expression by ambient pH are to be found in the animal kingdom. The potential applied importance of this regulatory system lies in its key role in fungal pathogenicity of animals and plants and in its control of fungal production of toxins, antibiotics, and secreted enzymes.

Cellular biosensing system for discovery of protein synthesis inhibitors with an electrochemical phosphate modulator to regulate the acid phosphatase gene expression of Saccharomyces cerevisiae

A cellular biosensing system for screening protein synthesis inhibitors has been developed by linking an electrochemical phosphate modulator and matrix-immobilized yeast cells with an optical sensing device. To screen the protein synthesis inhibitors, yeast phosphatase gene regulating system has been employed by linking an electrochemical phosphate modulator. Since the yeast phosphatase gene coding gammaAPase is expressed, when the phosphate concentration in solution is lowered below the threshold, the gammaAPase production is triggered by lowering the phosphate concentration with the electrochemical phosphate modulator, and monitored continuously with the photometric device. The electrochemical phosphate modulator was assembled with matrix-immobilized yeast cells. The module could insert to ordinal cuvette to monitor the induced gammaAPase activity in an ordinal photometer. Using the system, induction profile of protein synthesis was easily observed and was affected remarkably by various protein synthesis inhibitors. This seems promising that the system can be applied for first screening process of de novo protein inhibitors. The cellular biosensing system seems promising in screening protein synthesis inhibitors.

Synthesis of glia-derived nexin in yeast

Glia-derived nexin (GDN) is a 43-kDa glycoprotein isolated from rat glioma cell cultures. It promotes neurite extension in cultures of neuroblastoma cells and chick sympathetic neurons. Moreover, GDN is a potent serine protease inhibitor (serpin), belonging to the family of protease nexins. We report here the expression of rat GDN in the Saccharomyces cerevisiae strain GRF18 under the control of the PHO5 promoter. We describe the purification of more than 6 mg total GDN from the cellular extract of 1 liter of yeast culture. The amino acid composition and the sequence of CNBr-fragments of the recombinant protein correlate with the values deduced from the rat GDN cDNA. We provide evidence that the recombinant GDN has exactly the same properties as the glioma-derived protein with respect to its protease-inhibitory activity and its ability to promote the extension of neurites from neuroblastoma cells. The large amounts of recombinant protein obtained from this expression system will allow further biochemical and physiological analysis of GDN and of the serpins in general.

Maintenance of cytoplasmic pH and proton motive force in promastigotes of Leishmania donovani

Three methods were used to measure intracellular pH (pHi) of Leishmania donovani promastigotes: (a) measurement of the fluorescence of the pH indicator 2',7'-bis-(carboxyethyl)-5,6-carboxyfluorescein; (b) pH null point assays; and (c) determination of the distribution across the promastigote plasma membrane of the fluorescent amine acridine orange and of the weak acid 5,5-dimethyl-2,4-oxazolidinedione. The three methods gave similar results and showed that promastigotes of L. donovani maintain pHi at a narrow range of 6.4-6.7, throughout an extracellular pH (pHo) range of 5.5-7.4. L-Proline transport in L. donovani promastigotes, which is known to be coupled to proton translocation, was used to estimate the proton electrochemical gradient across parasite plasma membrane. While proline uptake is optimal at pHo 7.5, an outward-directed concentration gradient is obtained at steady state throughout a pHo range of 5-8. The calculated electrochemical gradient of proline across the parasite plasma membrane at steady state is 90-100 mV within a pHo range of 5-8, suggesting an almost constant proton electrochemical gradient at this pHo range. Taken together, the results show that the parasites regulate both pHi and the size of the chemiosmotic energy required to drive active transport of nutrients.

Expression of human T-cell leukemia virus type I envelope protein in Saccharomyces cerevisiae

The entire envelope gene of human T-cell leukemia virus type I (HTLV-I) was inserted into an expression vector and expressed under the control of the repressible acid phosphatase promoter in yeast (Saccharomyces cerevisiae). The product in yeast cells was glycosylated into heterodisperse proteins.

RNA and homology mapping of two DNA fragments with repressible acid phosphatase genes from Saccharomyces cerevisiae

Two EcoRI restriction fragments carrying Saccharomyces cerevisiae repressible acid phosphatase genes were analyzed. Transcripts were mapped by restriction endonuclease cleavage of glyoxal-stabilized R-loops and by gel blot hybridizations to cDNA. Homology between the two fragments was examined by gel blots and heteroduplex analysis. Each fragment carried a region of about 1.5 kilobases that coded for a repressible acid phosphatase, and these regions showed homology to one another. In addition, one fragment carried a second region of somewhat lower homology that probably codes for the so-called constitutive acid phosphatase.

Comparative analysis of the 5'-end regions of two repressible acid phosphatase genes in Saccharomyces cerevisiae

The nucleotide sequence of 5'-noncoding and N-terminal coding regions of two coordinately regulated, repressible acid phosphatase genes from Saccharomyces cerevisiae were determined. These unlinked genes encode different, but structurally related polypeptides of molecular weights 60,000 and 56,000. The DNA sequences of their 5'-flanking regions show stretches of extensive homology upstream of, and surrounding, a "TATA" sequence and in a region in which heterogeneous 5' ends of the p60 mRNA were mapped. The predicted amino acid sequences encoded by the N-terminal regions of both genes were confirmed by determination of the amino acid sequence of the native exocellular acid phosphatase and the partial sequence of the presecretory polypeptide synthesized in a cell-free protein synthesizing system. The N-terminal region of the p60 polypeptide was shown to be characterized by a hydrophobic 17-amino acid signal polypeptide which is absent in the native exocellular protein and thought to be necessary for acid phosphatase secretion.

RNA and homology mapping of two DNA fragments with repressible acid phosphatase genes from Saccharomyces cerevisiae

Two EcoRI restriction fragments carrying Saccharomyces cerevisiae repressible acid phosphatase genes were analyzed. Transcripts were mapped by restriction endonuclease cleavage of glyoxal-stabilized R-loops and by gel blot hybridizations to cDNA. Homology between the two fragments was examined by gel blots and heteroduplex analysis. Each fragment carried a region of about 1.5 kilobases that coded for a repressible acid phosphatase, and these regions showed homology to one another. In addition, one fragment carried a second region of somewhat lower homology that probably codes for the so-called constitutive acid phosphatase.

Comparative analysis of the 5'-end regions of two repressible acid phosphatase genes in Saccharomyces cerevisiae

The nucleotide sequence of 5'-noncoding and N-terminal coding regions of two coordinately regulated, repressible acid phosphatase genes from Saccharomyces cerevisiae were determined. These unlinked genes encode different, but structurally related polypeptides of molecular weights 60,000 and 56,000. The DNA sequences of their 5'-flanking regions show stretches of extensive homology upstream of, and surrounding, a "TATA" sequence and in a region in which heterogeneous 5' ends of the p60 mRNA were mapped. The predicted amino acid sequences encoded by the N-terminal regions of both genes were confirmed by determination of the amino acid sequence of the native exocellular acid phosphatase and the partial sequence of the presecretory polypeptide synthesized in a cell-free protein synthesizing system. The N-terminal region of the p60 polypeptide was shown to be characterized by a hydrophobic 17-amino acid signal polypeptide which is absent in the native exocellular protein and thought to be necessary for acid phosphatase secretion.

Synthesis of repressible acid phosphatase in Saccharomyces cerevisiae under conditions of enzyme instability

The synthesis of repressible acid phosphatase in Saccharomyces cerevisiae was examined under conditions of blocked derepression as described by Toh-e et al. (Mol. Gen. Genet. 162:139-149, 1978). Based on a genetic and biochemical analysis of the phenomenon these authors proposed a new regulatory model for acid phosphatase expression involving a simultaneous interaction of regulatory factors in the control of structural gene transcription. We demonstrate here that under growth conditions that fail to produce acid phosphatase the enzyme is readily inactivated. Furthermore, we demonstrate under these conditions the production of acid phosphatase mRNA which is active both in vitro and in vivo in the synthesis of enzyme. This eliminates any step prior to translation of acid phosphatase polypeptide as an explanation for the phenomenon. We interpret our results for the block in appearance of acid phosphatase as a result of both deaccelerated growth and cellular biosynthesis during derepression, accompanied by an enhanced instability of the enzyme.

Differential regulation of the active and inactive forms of Saccharomyces cerevisiae acid phosphatase

Acid phosphatase in S. cerevisiae exists as an enzymatically active, cell wall associated form and as an enzymatically inactive, probably membrane-bound form (Schweingruber and Schweingruber, in press). Orthophosphate dependent and independent regulation determines the level of acid phosphatase activity. To deduce the regulation mechanisms we purified and quantified active and inactive acid phosphatase from cells grown under different physiological conditions and displaying variable levels of enzyme activity. Orthophosphate dependent regulation does not include significant changes in the amount of total (active and inactive) acid phosphatase protein synthesized. Under the experimental conditions chosen increased activity is achieved by preferential synthesis of the active form and by increasing the specific activity of the active enzyme. Orthophosphate independent regulation seems to occur by similar mechanisms.

Cyclic AMP may not be involved in catabolite repression in Saccharomyes cerevisiae: evidence from mutants capable of utilizing it as an adenine source

Mutants able to utilize 5'-AMP or cyclic AMP as the adenine source were isolated from an ade6 ade10 double mutant by ethyl methane sulfonate mutagenesis. A single amp1 mutation, primarily selected on 5'-AMP medium, confers the phenotype for utilization of exogenous 5'-AMP as the adenine source. From the ade6 ade10 amp1 triple mutant, a mutant able to utilize cyclic AMP was isolated, and the mutant phenotype was proven to be due to the simultaneous occurrence of triple mutations designated as cam1, cam2, and cam3. The cam3 mutation, but not cam1 or cam2, also confers the phenotype for utilizing 5'-AMP, the same phenotype as the amp1 mutation. All of these mutations are recessive to the respective wild-type counterparts. Cells having the ade6 ade10 amp1 cam1 cam2 cam3 genotype showed significant ability to take up exogenous cyclic AMP, whereas no differences were observed in cyclic AMP phosphodiesterase activity in comparison with that of the original strains used in the mutant isolation. Since glucose severely repressed galactokinase synthesis in the constitutive GAL81 mutant having the ade6 ade10 amp1 cam1 cam2 cam3 genotype, irrespective of the presence or absence of cyclic AMP in the medium, it was suggested that cyclic AMP is not involved in the mechanism of catabolite repression in Saccharomyces cerevisiae. It does, however, have a stimulative effect on the galactokinase synthesis in the GAL81 mutant in the absence of glucose.

Synthesis of repressible acid phosphatase in Saccharomyces cerevisiae under conditions of enzyme instability

The synthesis of repressible acid phosphatase in Saccharomyces cerevisiae was examined under conditions of blocked derepression as described by Toh-e et al. (Mol. Gen. Genet. 162:139-149, 1978). Based on a genetic and biochemical analysis of the phenomenon these authors proposed a new regulatory model for acid phosphatase expression involving a simultaneous interaction of regulatory factors in the control of structural gene transcription. We demonstrate here that under growth conditions that fail to produce acid phosphatase the enzyme is readily inactivated. Furthermore, we demonstrate under these conditions the production of acid phosphatase mRNA which is active both in vitro and in vivo in the synthesis of enzyme. This eliminates any step prior to translation of acid phosphatase polypeptide as an explanation for the phenomenon. We interpret our results for the block in appearance of acid phosphatase as a result of both deaccelerated growth and cellular biosynthesis during derepression, accompanied by an enhanced instability of the enzyme.

Isolation of yeast genes with mRNA levels controlled by phosphate concentration

A library of DNA from the yeast, Saccharomyces cerevisiae, was constructed in phage lambda Charon 4 vector and then screened by differential plaque filter hybridization for genes induced by phosphate starvation. Two EcoRI fragments of 7.9 and 5.0 kilobase pairs that contained such genes were isolated. These cloned fragments may each carry one of the several copies of the genes for the repressible acid phosphatase of yeast. The fragments were use to examine mRNA levels of these genes in regulatory mutants of acid phosphatase.

In vitro synthesis of repressible yeast acid phosphatase: identification of multiple mRNAs and products

Antibodies to repressible nonspecific acid phosphatase [APase; orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2] purified from Saccharomyces cerevisiae were used to detect the in vitro products of APase mRNA. Immunoprecipitation of cell-free synthesized protein and of in vivo enzyme from cell extracts has shown that derepression of enzyme synthesis in situ is the result of de novo appearance of functional mRNA followed by de novo protein synthesis. At least three unique APase polypeptides are synthesized in vitro from separate mRNAs and appear to be glycosylated in vivo to form secreted enzyme.

Function of positive regulatory gene gal4 in the synthesis of galactose pathway enzymes in Saccharomyces cerevisiae: evidence that the GAL81 region codes for part of the gal4 protein

A meiotic fine structure map of the gal4 locus was constructed, which extended over 0.44 units on the chromosome (units in percent frequency of supposed recombination). Several nonsense gal4 mutations (four UAA and two supposed UGA [gal4-62 and gal4-69]) were placed at various sites on the map. In reversion experiments with 20 independently isolated gal4 mutants, only the gal4-62 and gal4-69 alleles, which are located at the same site on the map, could revert to overcome the superrepression of gal80s-1 spontaneously with a frequency of approximately 4 x 10(-7). Secondary mutations in the revertants occurred in the region of gal4-62 or were due to unlinked suppressors. A total of 15 GAL81 mutations in 19 isolates were found to be located in the same region as gal4-62 by three-point crosses with the aid of gal4 mutants; the other four could not be analyzed. The reverted gal4 gene and GAL81 mutations were semidominant over the wild-type GAL4+ allele and fully dominant over a nonsense gal4 mutation. Four suppressors (one dominant and three recessive) effective against gal4-62 and gal4-69 were isolated. The dominant suppressor was also effective against three independent, authentic auxotrophic UGA nonsense mutations, and one of the three recessive suppressors were effective against the authentic auxotrophic UAA and UAG mutations. These results strongly support the idea that the gal4 locus is expressed constitutively and codes for a regulatory protein. The GAL81 site mapped inside the locus codes for a part of the gal4 protein but does not work as an operator.

Posttranslational regulation of repressible acid phosphatase in yeast

On the basis of genetic data it has been suggested that repressible acid phosphatase of Saccharomyces cerevisiae is regulated by a control circuit involving operator-repressor mechanisms (Toh-e et al., 1978). We measured no significant difference in the amount of translatable mRNA of repressed and derepressed cells in the reticulocyte in vitro translation system. We find a 25 fold difference in specific enzyme activity in repressed versus derepressed cells whereas the amount of 35S-methionine labelled enzyme protein as measured by antibody precipitation varies only 2-3 fold. This argues for posttranslational regulation of preexisting inactive acid phosphatase. Minor regulatory effects at the transcriptional or translational level cannot be excluded.