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

Evidence for transcriptional regulation of dihydroorotic acid dehydrogenase in Saccharomyces cerevisiae

Two yeast DNA fragments carrying the URA 1 gene have been isolated. URA 1 mRNA levels were measured in wild-type yeast and ppr 1 (constitutive for DHOdehase synthesis) strains. Results favour the hypothesis that ppr 1 increases the transcription of URA 1. The corresponding E. coli PYR D gene has also been cloned.

Genetic instability of constitutive acid phosphatase in shochu and sake yeast

Genetic instability of constitutive acid phosphatase (cAPase) activity was observed in a shochu brewer's yeast strain (Ko), which consistently produced 0.3-1% progeny without cAPase when it had been subcultured for a long period of time in barley shochu mash or in conventional complete medium. Genetic analysis showed that the cAPase-negative phenotype was associated with a single mutation in the PHO3 gene and that the Ko strain had heteroallelic PHO3/pho3 genes, while the PHO3⁻ mutants had the homoallelic pho3/pho3 defect. Some sake yeast strains that are cAPase negative, such as K6, K7 and K9, also had the same homoallelic defect, whereas another sake yeast strain K3, with heteroallelic PHO3/pho3 genes, displayed similar genetic instability of cAPase activity. In all cases, the pho3-defective genes were generated by deletion of an approximately 1.9 kb region between the PHO5-PHO3 tandem genes on chromosome II, resulting in chimeric PHO5/3 fusion genes with different fusion points. By integrating a lys2 marker, which is linked with the pho3 allele on the arm of chromosome II in the Ko strain, we demonstrated that the pho3/pho3 defect originated either from a loss of heterozygosity at the heteroallelic PHO3/pho3 locus or from a looping out of the PHO3 region. Although fermentation experiments have not yet indicated any correlation between cAPase activity and alcohol production, the PHO3⁻ mutation itself could prove to be a useful selective marker for yeast strains carrying a number of advantageous mutations for fermentation and which display phenotypic diversity and stability.

Acid phosphatases of budding yeast as a model of choice for transcription regulation research

Acid phosphatases of budding yeast have been studied for more than forty years. This paper covers biochemical characteristics of acid phosphatases and different aspects in expression regulation of eukaryotic genes, which were researched using acid phosphatases model. A special focus is devoted to cyclin-dependent kinase Pho85p, a negative transcriptional regulator, and its role in maintaining mitochondrial genome stability and to pleiotropic effects of pho85 mutations.

Inorganic phosphate as an important regulator of phosphatases

Cellular metabolism depends on the appropriate concentration of intracellular inorganic phosphate (Pi). Pi starvation-responsive genes appear to be involved in multiple metabolic pathways, implying a complex Pi regulation system in microorganisms and plants. A group of enzymes is required for absorption and maintenance of adequate phosphate levels, which is released from phosphate esters and anhydrides. The phosphatase system is particularly suited for the study of regulatory mechanisms because phosphatase activity is easily measured using specific methods and the difference between the repressed and derepressed levels of phosphatase activity is easily detected. This paper analyzes the protein phosphatase system induced during phosphate starvation in different organisms.

The Pho80-like cyclin of Aspergillus nidulans regulates development independently of its role in phosphate acquisition

In Saccharomyces cerevisiae, phosphate acquisition enzymes are regulated by a cyclin-dependent kinase (Pho85), a cyclin (Pho80), the cyclin-dependent kinase inhibitor Pho81, and the helix-loop-helix transcription factor Pho4 (the PHO system). Previous studies in Aspergillus nidulans indicate that a Pho85-like kinase, PHOA, does not regulate the classic PHO system but regulates development in a phosphate-dependent manner. A Pho80-like cyclin has now been isolated through its interaction with PHOA. Surprisingly, unlike PHOA, An-PHO80 does play a negative role in the PHO system. Similarly, an ortholog of Pho4 previously identified genetically as palcA also regulates the PHO system. However, An-PHO81, a putative cyclin-dependent kinase inhibitor, does not regulate the PHO system. Therefore, there are significant differences between the classic PHO system conserved between S. cerevisiae and Neurospora crassa compared with that which has evolved in A. nidulans. Most interestingly, under low phosphate conditions, the An-PHO80 cyclin also promotes sexual development while having a negative effect on asexual development. These effects are independent of the role An-PHO80 has in the classic PHO system. However, in high phosphate medium, An-PHO80 affects development because of deregulation of the PHO system as loss of palcA(Pho4) function negates the developmental defects caused by lack of An-pho80. Therefore, under low phosphate conditions the An-PHO80 cyclin regulates development independently of the PHO system, whereas in high phosphate it affects development through the PHO system. The data indicate that a single cyclin can control various aspects of growth and development in a multicellular organism.

Identification of proteins whose synthesis is modulated during the cell cycle of Saccharomyces cerevisiae

We examined the synthesis and turnover of individual proteins in the Saccharomyces cerevisiae cell cycle. Proteins were pulse-labeled with radioactive isotope (35S or 14C) in cells at discrete cycle stages and then resolved on two-dimensional gels and analyzed by a semiautomatic procedure for quantitating gel electropherogram-autoradiographs. The cells were obtained by one of three methods: (i) isolation of synchronous subpopulations of growing cells by zonal centrifugation.; (ii) fractionation of pulse-labeled steady-state cultures according to cell age; and (iii) synchronization of cells with the mating pheromone, alpha-factor. In confirmation of previous studies, we found that the histones H4, H2A, and H2B were synthesized almost exclusively in the late G1 and early S phases. In addition, we identified eight proteins whose rates of synthesis were modulated in the cell cycle, and nine proteins (of which five, which may well be related, were unstable, with half-lives of 10 to 15 min) that might be regulated in the cell cycle by periodic synthesis, modification, or degradation. Based on the time of maximal labeling in the cell cycle and on experiments with alpha-factor and hydroxyurea, we assigned the cell cycle proteins to two classes: proteins in class I were labeled principally in early G1 phase and at a late stage of the cycle, whereas those in class II were primarily synthesized at times ranging from late G1 to mid S phase. At least one major control point for the cell cycle proteins occurred between "start" and early S phase. A set of stress-responsive proteins was also identified and analyzed. The rates of synthesis of these proteins were affected by certain perturbations that resulted during selection of synchronous cell populations and by heat shock.

Identification of proteins whose synthesis is modulated during the cell cycle of Saccharomyces cerevisiae

We examined the synthesis and turnover of individual proteins in the Saccharomyces cerevisiae cell cycle. Proteins were pulse-labeled with radioactive isotope (35S or 14C) in cells at discrete cycle stages and then resolved on two-dimensional gels and analyzed by a semiautomatic procedure for quantitating gel electropherogram-autoradiographs. The cells were obtained by one of three methods: (i) isolation of synchronous subpopulations of growing cells by zonal centrifugation.; (ii) fractionation of pulse-labeled steady-state cultures according to cell age; and (iii) synchronization of cells with the mating pheromone, alpha-factor. In confirmation of previous studies, we found that the histones H4, H2A, and H2B were synthesized almost exclusively in the late G1 and early S phases. In addition, we identified eight proteins whose rates of synthesis were modulated in the cell cycle, and nine proteins (of which five, which may well be related, were unstable, with half-lives of 10 to 15 min) that might be regulated in the cell cycle by periodic synthesis, modification, or degradation. Based on the time of maximal labeling in the cell cycle and on experiments with alpha-factor and hydroxyurea, we assigned the cell cycle proteins to two classes: proteins in class I were labeled principally in early G1 phase and at a late stage of the cycle, whereas those in class II were primarily synthesized at times ranging from late G1 to mid S phase. At least one major control point for the cell cycle proteins occurred between "start" and early S phase. A set of stress-responsive proteins was also identified and analyzed. The rates of synthesis of these proteins were affected by certain perturbations that resulted during selection of synchronous cell populations and by heat shock.

Regulation of phosphate acquisition in Saccharomyces cerevisiae

Membrane transport systems active in cellular inorganic phosphate (P(i)) acquisition play a key role in maintaining cellular P(i) homeostasis, independent of whether the cell is a unicellular microorganism or is contained in the tissue of a higher eukaryotic organism. Since unicellular eukaryotes such as yeast interact directly with the nutritious environment, regulation of P(i) transport is maintained solely by transduction of nutrient signals across the plasma membrane. The individual yeast cell thus recognizes nutrients that can act as both signals and sustenance. The present review provides an overview of P(i) acquisition via the plasma membrane P(i) transporters of Saccharomyces cerevisiae and the regulation of internal P(i) stores under the prevailing P(i) status.

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.

Acclimation of Chlamydomonas reinhardtii to its nutrient environment

To cope with low nutrient availability in nature, organisms have evolved inducible systems that enable them to scavenge and efficiently utilize the limiting nutrient. Furthermore, organisms must have the capacity to adjust their rate of metabolism and make specific alterations in metabolic pathways that favor survival when the potential for cell growth and division is reduced. In this article I will focus on the acclimation of Chlamydomonas reinhardtii, a unicellular, eukaryotic green alga to conditions of nitrogen, sulfur and phosphorus deprivation. This organism has a distinguished history as a model for classical genetic analyses, but it has recently been developed for exploitation using an array of molecular and genomic tools. The application of these tools to the analyses of nutrient limitation responses (and other biological processes) is revealing mechanisms that enable Chlamydomonas to survive harsh environmental conditions and establishing relationships between the responses of this morphologically simple, photosynthetic eukaryote and those of both nonphotosynthetic organisms and vascular plants.

N-glycosylation does not affect assembly and targeting of proglycinin in yeast

Glycinin, a simple protein, and beta-conglycinin, a glycoprotein, are the dominant storage proteins of soybean and are suggested to be derived from a common ancestor. To investigate why glycinin does not require glycosylation for its maturation, we attempted N-glycosylation of proglycinin A1aB1b using site-directed mutagenesis and yeast expression system. An N-glycosylation consensus sequence Asn-X-Ser/Thr was created at positions 103, 183, 196, 284 and 457 in the variable regions being strongly hydrophilic revealed from the alignment of amino acid sequences of various glycinin-type proteins. Among five mutant proglycinins (Q103N, H183N, G198T, S284N, N459T), Q103N was fully glycosylated, and H183N and N459T were partly (around 20% of the expressed proteins), whereas others were barely or not glycosylated. The glycosylated proglycinin was susceptible to endo-beta-N-acetylglucosamidase and N-glycanase cleavages. N-glycosylation did not cause inconveniences to processing of signal peptide, assembly into trimers and targeting into the vacuoles. Thermal and trypsin sensitivity analyses of the glycosylated proglycinin suggested that N-linked glycan prevents protein-protein interaction but does not stabilize the protein conformation. The reason why glycinin does not require N-glycosylation for its maturation is discussed.

Homeodomain-DNA interactions of the Pho2 protein are promoter-dependent

The homeodomain (HD) is a conserved sequence-specific DNA-binding motif found in many eukaryotic transcriptional regulatory proteins. Despite the wealth of in vitro data on the mechanism HD proteins use to bind DNA, comparatively little is known about the roles of individual residues in these domains in vivo . The Saccharomyces cerevisiae Pho2 protein contains a HD that shares significant sequence identity with the Drosophila Engrailed protein. We have used the co-crystal structure of Engrailed as a model to predict how Pho2 might contact DNA and have examined how individual residues of the Pho2 HD contribute to transcriptional activation in vivo and to DNA binding in vitro. Our results demonstrate that Pho2 and Engrailed share many similar DNA-binding characteristics. However, our results also show that some highly conserved residues, which contact the DNA in many HD structures, make relatively small contributions to the DNA-binding affinity and in vivo activity of the Pho2 protein. We also show that the N-terminal arm of the Pho2 HD is a critical component in determining the DNA-binding specificity of the protein and that the requirements for residues in the N-terminal arm are promoter-dependent for Pho2 transcriptional activation and DNA binding.

The phosphatase system in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae has at least six species of acid and alkaline phosphatases with different cellular localizations, as well as inorganic phosphate (Pi) transporters. Most of the genes encoding these enzymes are coordinately repressed and derepressed depending on the Pi concentration in the growth medium. The Pi signals are conveyed to these genes through a regulatory circuit consisting of a set of positive and negative regulatory proteins. This phosphatase system is interested as one of the best systems for studying gene regulation in S. cerevisiae due to the simplicity of phenotype determination in genetic analysis. With this methodological advantage, considerable amounts of genetic and molecular evidence in phosphatase regulation have been accumulated in the past twenty-five years. This article summarizes the current progress of research into this subject.

Morphogenesis of the glomerular filter: the synchronous assembly and maturation of two distinct extracellular matrices

The morphogenesis of the glomerular filtration apparatus during pre- and postnatal development in the rodent involves the coordinated assembly of two closely apposed but morphologically different extracellular matrices, the glomerular capillary basement membrane and the mesangial matrix. The cellular origin of these matrices is known to be distinct and complex; however, the mechanisms by which these matrices are assembled during morphogenesis are not entirely understood. It has been shown that in the earliest stages of glomerular morphogenesis the nascent glomerular basement membrane exists as a four-layered structure, the product of both the visceral epithelium and capillary endothelium. During the latter stages of glomerular development, the quadrilaminar structure becomes a trilaminar basement membrane, the event thought to occur by fusion of closely apposed basement membrane layers. In subsequent stages of maturation and throughout the life of the animal, the visceral epithelial cells, which line the periphery of the glomerular capillary, are the primary source of newly synthesized basement membrane material. The mesangial matrix, which lacks the specific organization of a basement membrane, first occurs in the developing glomerulus as a diffuse matrix central to the developing glomerular capillaries. During glomerular maturation the mesangial matrix undergoes a compaction/arborization coincident with the ramification of the vascular histoarchitecture of the glomerular tuft. Recent advances in the cell biology of basement membrane now demonstrate that there is a divergence in isoforms of the molecules that comprise the glomerular capillary basement membrane and mesangial matrices during development, possibly coincidental with functional specialization during the process of glomerular maturation.

The KIPHO5 gene encoding a repressible acid phosphatase in the yeast Kluyveromyces lactis: cloning, sequencing and transcriptional analysis of the gene, and purification and properties of the enzyme

A secreted phosphate-repressible acid phosphatase from Kluyveromyces lactis has been purified and the N-terminal region and an internal peptide have been sequenced. Using synthetic oligodeoxyribonucleotides based on the sequenced regions, the genomic sequence, KIPHO5, encoding the protein has been isolated. The deduced protein, named KIPho5p, consists of 469 amino acids and has a molecular mass of 52520 Da (in agreement with the data obtained after treatment of the protein with endoglycosidase H). The purified enzyme shows size heterogeneity, with an apparent molecular mass in the range 90-200 kDa due to the carbohydrate content (10 putative glycosylation sites were identified in the sequence). A 16 amino acid sequence at the N-terminus is similar to previously identified signal peptides in other fungal secretory proteins. The putative signal peptide is removed during secretion since it is absent in the mature secreted acid phosphatase. The gene can be induced 400-600-fold by phosphate starvation. Consensus signals corresponding to those described for Saccharomyces cerevisiae PHO4- and PHO2-binding sites are found in the 5' region. Northern blot analysis of total cellular RNA indicates that the KIPHO5 gene codes for a 1.8 kb transcript and that its expression is regulated at the transcriptional level. Chromosomal hybridization indicated that the gene is located on chromosome II. The KIPHO5 gene of K. lactis is able to functionally complement a pho5 mutation of Sacch. cerevisiae. Southern blot experiments, using the KIPHO5 gene as probe, show that some K. lactis reference strains lack repressible acid phosphatase, revealing a different gene organization for this kind of multigene family of proteins as compared to Sacch. cerevisiae.

Biochemical properties and excretion behavior of repressible acid phosphatases with altered subunit composition

Yeast repressible acid phosphatase (rAP) is the oligomeric extracellular enzyme encoded by the three structural genes PH05 (p60), PHO10 (p58) and PHO11 (p56). We examined the ability of acid phosphatases formed by various subunit combinations to be excreted into the medium. Plasmids with repressible acid phosphatase structural genes under control of the yeast glyceraldehyde-phosphate dehydrogenase (GAP) promoter were constructed to obtain constitutive expression of acid phosphatase, and yeast strains with disruptions in PHO5, PHO10 and PHO11, respectively, were used to generate mutants expressing single genes or specific gene combinations. EndoF treatment of acid phosphatases, produced by these strains, followed by SDS-electrophoresis in combination with densitometry techniques revealed that the ratio p60/(p56 + p58) among structural polypeptides in extracellular enzyme is constant and equals to 6.0. A study of acid phosphatases formed by single type subunits was undertaken. Expression products of PHO5, PHO10 and PHO11 genes were isolated from the culture medium. The specific activities of the enzymes were found to be 33, 2 and 2 mM x mg-1 x min-1, respectively. The values of Mr estimated by HPLC chromatography for the enzymes encoded for by the genes PHO5, PHO10 and PHO11 and SDS-polyacrilamide gel electrophoresis data suggested an oligomeric organisation of the enzymes. Isoelectric focusing in polyacrylamide gel with immobilised pH gradient followed by activity staining yielded numerous sharp bands of homopolymeric acid phosphatases forms being different in their pI. The kinetic characterisation of the enzymes revealed differences in Km values, sensitivity to temperature inactivation, inhibition by orthophosphate and the effect of pH on the enzyme activity.

Deletion of the gene encoding the cyclin-dependent protein kinase Pho85 alters glycogen metabolism in Saccharomyces cerevisiae

Pho85, a protein kinase with significant homology to the cyclin-dependent kinase, Cdc28, has been shown to function in repression of transcription of acid phosphatase (APase, encoded by PHO5) in high phosphate (Pi) medium, as well as in regulation of the cell cycle at G1/S. We described several unique phenotypes associated with the deletion of the PHO85 gene including growth defects on a variety of carbon sources and hyperaccumulation of glycogen in rich medium high in Pi. Hyperaccumulation of glycogen in the pho85 strains is independent of other APase regulatory molecules and is not signaled through Snfl kinase. However, constitutive activation of cAPK suppresses the hyperaccumulation of glycogen in a pho85 mutant. Mutation of the type-1 protein phosphatase encoded by GLC7 only partially suppresses the glycogen phenotype of the pho85 mutant. Additionally, strains containing a deletion of the PHO85 gene show an increase in expression of GSY2. This work provides evidence that Pho85 has functions in addition to transcriptional regulation of APase and cell-cycle progression including the regulation of glycogen levels in the cell and may provide a link between the nutritional state of the cell and these growth related responses.

Genetic and carbon source regulation of phosphorylation of Sip1p, a Snf1p-associated protein involved in carbon response in Saccharomyces cerevisiae

The SIP1 gene of Saccharomyces cerevisiae is a carbon-catabolite-specific negative regulator of GAL gene transcription and acts as a multicopy suppressor of growth defects associated with impaired Snf1p protein kinase activity. The Sip1 protein is known to undergo phosphorylation when associated in vitro with the Snf1 protein kinase. We have carried out in vivo studies of the genetic and carbon control of Sip1p phosphorylation. Metabolic labeling reveals phosphorylation of Sip1p under both carbon catabolite-repressing and non-repressing conditions and in both SNF1 wild-type and snf1-deletion cells. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblot assay, we detect apparent changes in Sip1p phosphorylation states in response to changes in carbon source. At least one dephosphorylation of Sip1p occurs with a shift from non-repressing carbon source to repressing carbon source. The MIG1 gene, acting through SNF1-dependent and SNF1-independent pathways, is required for some Sip1p phosphorylations. REG1 appears to be required for at least one dephosphorylation of Sip1p, whereas SSN6 appears to be required for at least one phosphorylation of Sip1p. These results reveal new complexities in carbon response signaling, and may reflect the involvement of the Sip1 protein in the same complex as the Mig1 and Ssn6 proteins.

Myocyte nuclear factor, a novel winged-helix transcription factor under both developmental and neural regulation in striated myocytes

A sequence motif (CCAC box) within an upstream enhancer region of the human myoglobin gene is essential for transcriptional activity in both cardiac and skeletal muscle. A cDNA clone, myocyte nuclear factor (MNF), was isolated from a murine expression library on the basis of sequence-specific binding to the myoglobin CCAC box motif and was found to encode a novel member of the winged-helix or HNF-3/fork head family of transcription factors. Probes based on this sequence identify two mRNA species that are upregulated during myocyte differentiation, and antibodies raised against recombinant MNF identify proteins of approximately 90, 68, and 65 kDa whose expression is regulated following differentiation of myogenic cells in culture. In addition, the 90-kDa form of MNF is phosphorylated and is upregulated in intact muscles subjected to chronic motor nerve stimulation, a potent stimulus to myoglobin gene regulation. Amino acid residues 280 to 389 of MNF demonstrate 35 to 89% sequence identity to the winged-helix domain from other known members of this family, but MNF is otherwise divergent. A proline-rich amino-terminal region (residues 1 to 206) of MNF functions as a transcriptional activation domain. These studies provide the first evidence that members of the winged-helix family of transcription factors have a role in myogenic differentiation and in remodeling processes of adult muscles that occur in response to physiological stimuli.

Myocyte nuclear factor, a novel winged-helix transcription factor under both developmental and neural regulation in striated myocytes

A sequence motif (CCAC box) within an upstream enhancer region of the human myoglobin gene is essential for transcriptional activity in both cardiac and skeletal muscle. A cDNA clone, myocyte nuclear factor (MNF), was isolated from a murine expression library on the basis of sequence-specific binding to the myoglobin CCAC box motif and was found to encode a novel member of the winged-helix or HNF-3/fork head family of transcription factors. Probes based on this sequence identify two mRNA species that are upregulated during myocyte differentiation, and antibodies raised against recombinant MNF identify proteins of approximately 90, 68, and 65 kDa whose expression is regulated following differentiation of myogenic cells in culture. In addition, the 90-kDa form of MNF is phosphorylated and is upregulated in intact muscles subjected to chronic motor nerve stimulation, a potent stimulus to myoglobin gene regulation. Amino acid residues 280 to 389 of MNF demonstrate 35 to 89% sequence identity to the winged-helix domain from other known members of this family, but MNF is otherwise divergent. A proline-rich amino-terminal region (residues 1 to 206) of MNF functions as a transcriptional activation domain. These studies provide the first evidence that members of the winged-helix family of transcription factors have a role in myogenic differentiation and in remodeling processes of adult muscles that occur in response to physiological stimuli.

Glucose repression of the yeast ADH2 gene occurs through multiple mechanisms, including control of the protein synthesis of its transcriptional activator, ADR1

The rate of ADH2 transcription increases dramatically when Saccharomyces cerevisiae cells are shifted from glucose to ethanol growth conditions. Since ADH2 expression under glucose growth conditions is strictly dependent on the dosage of the transcriptional activator ADR1, we investigated the possibility that regulation of the rate of ADR1 protein synthesis plays a role in controlling ADR1 activation of ADH2 transcription. We found that the rate of ADR1 protein synthesis increased 10- to 16-fold within 40 to 60 min after glucose depletion, coterminous with initiation of ADH2 transcription. Changes in ADR1 mRNA levels contributed only a twofold effect on ADR1 protein synthetic differences. The 510-nt untranslated ADR1 mRNA leader sequence was found to have no involvement in regulating the rate of ADR1 protein synthesis. In contrast, sequences internal to ADR1 coding region were determined to be necessary for controlling ADR1 translation. The ADR1c mutations which enhance ADR1 activity under glucose growth conditions did not affect ADR1 protein translation. ADR1 was also shown to be multiply phosphorylated in vivo under both ethanol and glucose growth conditions. Our results indicate that derepression of ADH2 occurs through multiple mechanisms involving the ADR1 regulatory protein.

Glucose repression of the yeast ADH2 gene occurs through multiple mechanisms, including control of the protein synthesis of its transcriptional activator, ADR1

The rate of ADH2 transcription increases dramatically when Saccharomyces cerevisiae cells are shifted from glucose to ethanol growth conditions. Since ADH2 expression under glucose growth conditions is strictly dependent on the dosage of the transcriptional activator ADR1, we investigated the possibility that regulation of the rate of ADR1 protein synthesis plays a role in controlling ADR1 activation of ADH2 transcription. We found that the rate of ADR1 protein synthesis increased 10- to 16-fold within 40 to 60 min after glucose depletion, coterminous with initiation of ADH2 transcription. Changes in ADR1 mRNA levels contributed only a twofold effect on ADR1 protein synthetic differences. The 510-nt untranslated ADR1 mRNA leader sequence was found to have no involvement in regulating the rate of ADR1 protein synthesis. In contrast, sequences internal to ADR1 coding region were determined to be necessary for controlling ADR1 translation. The ADR1c mutations which enhance ADR1 activity under glucose growth conditions did not affect ADR1 protein translation. ADR1 was also shown to be multiply phosphorylated in vivo under both ethanol and glucose growth conditions. Our results indicate that derepression of ADH2 occurs through multiple mechanisms involving the ADR1 regulatory protein.

The mechanism of inducer formation in gal3 mutants of the yeast galactose system is independent of normal galactose metabolism and mitochondrial respiratory function

Saccharomyces cerevisiae cells defective in GAL3 function exhibit either one of two phenotypes. The gal3 mutation in an otherwise normal cell causes a 2-5-day delay in the galactose triggered induction of GAL/MEL gene transcription. This long term adaptation (LTA) phenotype has been ascribed to inefficient inducer formation. The gal3 mutation causes a noninducible phenotype for GAL/MEL transcription if cells are defective in Leloir pathway function, in glycolysis or in respiratory function. It was recently shown that multiple copies of the intact GAL1 gene partially suppress the LTA phenotype of gal3 cells. Here we report that constitutively expressed GAL1 restored gal3 mutants to the rapidly inducible phenotype characteristic of wild-type cells and conferred rapid inducibility to gal3 gal10, gal3 gal7 or gal3 rho- strains that are normally noninducible. As shown by immunoblot analysis, the GAL1-mediated induction exhibits phosphorylation of the GAL4 protein, suggesting a mechanism similar to GAL3-mediated induction. Altogether our results indicate that the deciding factor in the inducibility of the GAL/MEL genes in gal3 strains is the Gal3p-like activity of Gal1p. Based on the above we conclude that inducer formation does not require normal metabolism of galactose nor does it require mitochondrial respiratory function. These conclusions vitiate previous explanations for gal3 associated long-term adaptation and noninducible phenotypes.

GAL11 (SPT13), a transcriptional regulator of diverse yeast genes, affects the phosphorylation state of GAL4, a highly specific transcriptional activator

The GAL4 protein of Saccharomyces cerevisiae is a DNA-binding transcriptional activator that is highly specific for the GAL genes. In vivo levels of GAL gene transcription are closely correlated with the phosphorylation state of GAL4. In vivo levels of GAL gene transcription are also affected by the activity of the GAL11 (SPT13) protein, a protein that has been implicated as a global auxiliary transcriptional factor. Here we examine the influence of GAL11 (SPT13) on the phosphorylation state of GAL4. Cells bearing a gal11 deletion mutation are defective in the production or maintenance of GAL4III, a phosphorylated form of GAL4 that is associated with higher levels of GAL gene transcription. In addition, the gal11 deletion cells are reduced in total GAL4 protein. However, the fivefold-reduced expression of the GAL1 gene observed in gal11 deletion cells cannot be due solely to reduced levels of total GAL4 protein, since gal11 deletion cells amplified for GAL4 production are still markedly reduced in GAL4 protein-dependent transcription. Thus, these data demonstrate that the GAL11 protein augments GAL4 protein-dependent transcription in a manner that is tightly coupled to the formation or maintenance of a phosphorylated form of GAL4.

GAL11 (SPT13), a transcriptional regulator of diverse yeast genes, affects the phosphorylation state of GAL4, a highly specific transcriptional activator

The GAL4 protein of Saccharomyces cerevisiae is a DNA-binding transcriptional activator that is highly specific for the GAL genes. In vivo levels of GAL gene transcription are closely correlated with the phosphorylation state of GAL4. In vivo levels of GAL gene transcription are also affected by the activity of the GAL11 (SPT13) protein, a protein that has been implicated as a global auxiliary transcriptional factor. Here we examine the influence of GAL11 (SPT13) on the phosphorylation state of GAL4. Cells bearing a gal11 deletion mutation are defective in the production or maintenance of GAL4III, a phosphorylated form of GAL4 that is associated with higher levels of GAL gene transcription. In addition, the gal11 deletion cells are reduced in total GAL4 protein. However, the fivefold-reduced expression of the GAL1 gene observed in gal11 deletion cells cannot be due solely to reduced levels of total GAL4 protein, since gal11 deletion cells amplified for GAL4 production are still markedly reduced in GAL4 protein-dependent transcription. Thus, these data demonstrate that the GAL11 protein augments GAL4 protein-dependent transcription in a manner that is tightly coupled to the formation or maintenance of a phosphorylated form of GAL4.

Molecular and expression analysis of the negative regulators involved in the transcriptional regulation of acid phosphatase production in Saccharomyces cerevisiae

The PHO80 and PHO85 gene products encode proteins necessary for the repression of transcription from the major acid phosphatase gene (PHO5) of Saccharomyces cerevisiae. The deduced amino acid sequences of these genes have revealed that PHO85 is likely to encode a protein kinase, whereas no potential function has been revealed for PHO80. We undertook several approaches to aid in the elucidation of the PHO80 function, including deletion analysis, chemical mutagenesis, and expression analysis. DNA deletion analysis revealed that residues from both the carboxy- and amino-terminal regions of the protein, amounting to a total of 21% of the PHO80 protein, were not required for function with respect to repressor activity. Also, 10 independent single-amino-acid changes within PHO80 which resulted in the failure to repress PHO5 transcription were isolated. Nine of the 10 missense mutations resided in two subregions of the PHO80 molecule. In addition, expression analysis of the PHO80 and PHO85 genes suggested that the PHO85 gene product was not necessary for PHO80 expression and that the PHO85 gene was expressed at much higher levels in the cell than was the PHO80 gene. Furthermore, high levels of PHO80 were shown to suppress the effect of a PHO85 deletion at a level close to full repression. Implications for the function of the negative regulators in this system are discussed.

New polypeptides and in-vitro-translatable mRNAs are produced by phosphate-starved cells of the unicellular algaChlamydomonas reinhardtii

Cells of the unicellular algaChlamydomonas reinhardtii Dang. deprived of inorganic phosphate (Pi) secrete into the culture medium large amounts of glycoproteins which are not produced by cells grown in the presence of Pi. One of the polypeptides (P6: Mr 73000 ± 2 000) resolved by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) is absent from a mutant lacking neutral-phosphatase activity, and probably corresponds to a subunit of this enzyme. The antibodies raised to P6, however, were able to cross-react on Western blots with most of the secreted proteins which indicates that they recognize oligosaccharide epitopes common to all of these de-novo-formed molecules. In order to verify whether the response to Pi deprivation takes place at the transcriptional level, the in-vitro translation products directed by poly(A)(+) RNA preparations obtained from cells grown with or without Pi were analyzed by two-dimensional SDS-PAGE. Three polypeptides specific to Pi-starved cells were detected but were considered unlikely to correspond to subunits of the neutral phosphatase. Whereas in-vivo-labelled proteins (notably P6) were precipitable by our antibodies, all attempts at precipitating in-vitro translation products have failed. This result is in agreement with the hypothesis that the antibodies recognize the oligosaccharide side chains but not the polypeptide backbone of the glycoproteins, a situation already described for monoclonal antibodies to the major structural glycoprotein of theChlamydomonas cell wall.

Molecular and expression analysis of the negative regulators involved in the transcriptional regulation of acid phosphatase production in Saccharomyces cerevisiae

The PHO80 and PHO85 gene products encode proteins necessary for the repression of transcription from the major acid phosphatase gene (PHO5) of Saccharomyces cerevisiae. The deduced amino acid sequences of these genes have revealed that PHO85 is likely to encode a protein kinase, whereas no potential function has been revealed for PHO80. We undertook several approaches to aid in the elucidation of the PHO80 function, including deletion analysis, chemical mutagenesis, and expression analysis. DNA deletion analysis revealed that residues from both the carboxy- and amino-terminal regions of the protein, amounting to a total of 21% of the PHO80 protein, were not required for function with respect to repressor activity. Also, 10 independent single-amino-acid changes within PHO80 which resulted in the failure to repress PHO5 transcription were isolated. Nine of the 10 missense mutations resided in two subregions of the PHO80 molecule. In addition, expression analysis of the PHO80 and PHO85 genes suggested that the PHO85 gene product was not necessary for PHO80 expression and that the PHO85 gene was expressed at much higher levels in the cell than was the PHO80 gene. Furthermore, high levels of PHO80 were shown to suppress the effect of a PHO85 deletion at a level close to full repression. Implications for the function of the negative regulators in this system are discussed.

Isolation and characterization of human reg protein produced in Saccharomyces cerevisiae

reg was originally identified as a gene expressed during the regeneration of insulin-producing pancreatic beta-cells of the rat. We built an expression vector containing human reg cDNA to drive Saccharomyces cerevisiae to synthesize the reg protein, and purified it from the culture medium. The 144-amino acid sequence of the recombinant protein was consistent with that deduced from the cDNA and genomic DNA sequence except that the signal sequence of 22 amino acids was eliminated, and the amino-terminal residue of the protein was pyroglutamic acid. The secondary structure of the reg protein was predicted by determination of the intramolecular cystine linkage and of alpha-helix and beta-sheet contents.

Phosphorylated forms of GAL4 are correlated with ability to activate transcription

GAL4I, GAL4II, and GAL4III are three forms of the yeast transcriptional activator protein that are readily distinguished on the basis of electrophoretic mobility during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Phosphorylation accounts for the reduced mobility of the slowest-migrating form, GAL4III, which is found to be closely associated with high-level GAL/MEL gene expression (L. Mylin, P. Bhat, and J. Hopper, Genes Dev. 3:1157-1165, 1989). Here we show that GAL4II, like GAL4III, can be converted to GAL4I by phosphatase treatment, suggesting that in vivo GAL4II is derived from GAL4I by phosphorylation. We found that cells which overproduced GAL4 under conditions in which it drove moderate to low levels of GAL/MEL gene expression showed only forms GAL4I and GAL4II. To distinguish which forms of GAL4 (GAL4I, GAL4II, or both) might be responsible for transcription activation in the absence of GAL4III, we performed immunoblot analysis on UASgal-binding-competent GAL4 proteins from four gal4 missense mutants selected for their inability to activate transcription (M. Johnston and J. Dover, Proc. Natl. Acad. Sci. USA 84:2401-2405, 1987; Genetics 120;63-74, 1988). The three mutants with no detectable GAL1 expression did not appear to form GAL4II or GAL4III, but revertants in which GAL4-dependent transcription was restored did display GAL4II- or GAL4III-like electrophoretic species. Detection of GAL4II in a UASgal-binding mutant suggests that neither UASgal binding nor GAL/MEL gene activation is required for the formation of GAL4II. Overall, our results imply that GAL4I may be inactive in transcriptional activation, whereas GAL4II appears to be active. In light of this work, we hypothesize that phosphorylation of GAL4I makes it competent to activate transcription.

Phosphorylated forms of GAL4 are correlated with ability to activate transcription

GAL4I, GAL4II, and GAL4III are three forms of the yeast transcriptional activator protein that are readily distinguished on the basis of electrophoretic mobility during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Phosphorylation accounts for the reduced mobility of the slowest-migrating form, GAL4III, which is found to be closely associated with high-level GAL/MEL gene expression (L. Mylin, P. Bhat, and J. Hopper, Genes Dev. 3:1157-1165, 1989). Here we show that GAL4II, like GAL4III, can be converted to GAL4I by phosphatase treatment, suggesting that in vivo GAL4II is derived from GAL4I by phosphorylation. We found that cells which overproduced GAL4 under conditions in which it drove moderate to low levels of GAL/MEL gene expression showed only forms GAL4I and GAL4II. To distinguish which forms of GAL4 (GAL4I, GAL4II, or both) might be responsible for transcription activation in the absence of GAL4III, we performed immunoblot analysis on UASgal-binding-competent GAL4 proteins from four gal4 missense mutants selected for their inability to activate transcription (M. Johnston and J. Dover, Proc. Natl. Acad. Sci. USA 84:2401-2405, 1987; Genetics 120;63-74, 1988). The three mutants with no detectable GAL1 expression did not appear to form GAL4II or GAL4III, but revertants in which GAL4-dependent transcription was restored did display GAL4II- or GAL4III-like electrophoretic species. Detection of GAL4II in a UASgal-binding mutant suggests that neither UASgal binding nor GAL/MEL gene activation is required for the formation of GAL4II. Overall, our results imply that GAL4I may be inactive in transcriptional activation, whereas GAL4II appears to be active. In light of this work, we hypothesize that phosphorylation of GAL4I makes it competent to activate transcription.

Deletion analysis of domain independence in the TRP1 gene product of Neurospora crassa

The trifunctional TRP1 gene from Neurospora crassa (N-TRP1) was subcloned into the yeast-Escherichia coli shuttle vector YEp13 and expressed in Saccharomyces cerevisiae. The three activities of the N-TRP1 gene product were detected in yeast mutants that lacked either N-(5'-phosphoribosyl) anthranilate (PRA) isomerase or both the glutamine amidotransferase function of anthranilate synthase and indole-3-glycerol phosphate (InGP) synthase. The protein was detected on immunoblots only as the full length 83 kda product indicating that the trifunctional gene product was expressed in yeast primarily in a fully active, undegraded form. By placing the subcloned N-TRP1 gene under the control of the inducible PHO5 promoter from yeast, the expression of all three activities was increased to more than ten fold that of wild-type yeast and the overproduced protein could be visualized by SDS-polyacrylamide gel electrophoresis of crude extract and Coomassie Blue staining. Using the expression system described the effect of selective deletion of regions of the coding sequence of the N-TRP1 gene on expression of the three activities was tested. Expression of either the F- or C-domains, catalyzing respectively the PRA isomerase or InGP synthase activities, did not depend on the presence of the other domain in the active polypeptide. Furthermore, normal dimer formation occurred with a protein active for InGP synthase in a deletion derivative lacking most of the PRA isomerase domain, ruling out the hypothesis that interaction between the active site regions for PRA isomerase and InGP synthase accounted for dimer formation in the trifunctional product.

A short domain of the plant vacuolar protein phytohemagglutinin targets invertase to the yeast vacuole

Phytohemagglutinin (PHA), the seed lectin of the common bean, accumulates in protein storage vacuoles of storage parenchyma cells in cotyledons. When expressed in yeast, PHA is efficiently targeted to the yeast vacuole [Tague and Chrispeels (1987). J. Cell Biol. 105, 1971-1979]. To identify vacuolar sorting information in PHA, a series of 3' deletions of the PHA gene were fused in-frame to a truncated yeast invertase gene. An amino-terminal portion of PHA composed of a 20-residue signal sequence and 43 residues of the mature protein efficiently targeted invertase to the yeast vacuole. Internal deletions in a short PHA-invertase fusion showed that targeting information exists between residues 14 and 23 of mature PHA. Based on examinations of three-dimensional structures of related lectins, only a portion of these residues would be available on the surface of PHA for interaction with a putative receptor. Amino acid replacements at these positions in a PHA-invertase hybrid caused secretion of the invertase. The results indicate the presence of a vacuolar targeting domain in PHA that is centered at position 19 of the mature protein. This sequence of PHA also shows sequence identity to a vacuolar sorting domain characterized in yeast carboxypeptidase Y. Single amino acid alterations in a short PHA-invertase hybrid protein that caused the highest levels of secretion introduced a glycosylation site at position 21 of PHA. This observation suggests that glycan addition may interfere with recognition of a sorting determinant. These same amino acid changes did not dramatically increase secretion in a long PHA-invertase fusion or in PHA itself. Thus, a second domain of PHA may function in concert with the first one to bring about correct targeting of PHA.

Analysis of the GAL3 signal transduction pathway activating GAL4 protein-dependent transcription in Saccharomyces cerevisiae

The Saccharomyces cerevisiae GAL/MEL regulon genes are normally induced within minutes of galactose addition, but gal3 mutants exhibit a 3-5-day induction lag. We have discovered that this long-term adaptation (LTA) phenotype conferred by gal3 is complemented by multiple copies of the GAL1 gene. Based on this result and the striking similarity between the GAL3 and GAL1 protein sequences we attempted to detect galactokinase activity that might be associated with the GAL3 protein. By both in vivo and in vitro tests the GAL3 gene product does not appear to catalyze a galactokinase-like reaction. In complementary experiments, Escherichia coli galactokinase expressed in yeast was shown to complement the gal1 but not the gal3 mutation. Thus, the complementation activity provided by GAL1 is not likely due to galactokinase activity, but rather due to a distinct GAL3-like activity. Overall, the results indicate that GAL1 encodes a bifunctional protein. In related experiments we tested for function of the LTA induction pathway in gal3 cells deficient for other gene functions. It has been known for some time that gal3gal1, gal3gal7, gal3gal10, and gal3 rho- are incapable of induction. We constructed isogenic haploid strains bearing the gal3 mutation in combination with either gal15 or pgi1 mutations: the gal15 and pgi1 blocks are not specific for the galactose pathway in contrast to the gal1, gal7 and gal10 blocks. The gal3gal5 and gal3pgi1 double mutants were not inducible, whereas both the gal5 and pgi1 single mutants were inducible. We conclude that, in addition to the GAL3-like activity of GAL1, functions beyond the galactose-specific GAL1, GAL7 and GAL10 enzymes are required for the LTA induction pathway.

Immunological characterization of a basement membrane-specific chondroitin sulfate proteoglycan

Reichert's membrane, an extraembryonic membrane present in developing rodents, has been proposed as an in vivo model for the study of basement membranes. We have used this membrane as a source for isolation of basement membrane proteoglycans. Reichert's membranes were extracted in a guanidine/3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate buffer followed by cesium chloride density-gradient ultracentrifugation under dissociative conditions. The proteoglycans were subsequently purified from the two most dense fractions (greater than 1.3 g/ml) by ion-exchange chromatography. Mice were immunized with the proteoglycan preparation and four mAbs recognizing the core protein of a high-density, buoyant chondroitin sulfate proteoglycan were raised. Confirmation of antibody specificity was carried out by the preparation of affinity columns made from each of the mAbs. Chondroitin sulfate proteoglycans (CSPGs) were purified from both supernatant and tissue fractions of Reichert's membranes incubated in short-term organ culture in the presence of radiolabel. The resultant affinity-purified proteoglycan samples were examined by gel filtration, SDS-PAGE, and immunoblotting. This proteoglycan is of high molecular weight (Mr = 5-6 x 10(5)), with a core protein of Mr = approximately 1.5-1.6 x 10(5) and composed exclusively of chondroitin sulfate chains with an average Mr = 1.6-1.8 x 10(4). In addition, a CSPG was purified from adult rat kidney, whose core protein was also Mr = 1.6 x 10(5). The proteoglycan and its core protein were also recognized by all four mAbs. Indirect immunofluorescence of rat tissue sections stained with these antibodies reveal a widespread distribution of this proteoglycan, localized specifically to Reichert's membrane and nearly all basement membranes of rat tissues. In addition to heparan sulfate proteoglycans, it therefore appears that at least one CSPG is a widespread basement membrane component.

Molecular cloning of chromosome I DNA from Saccharomyces cerevisiae: localization of a repeated sequence containing an acid phosphatase gene near a telomere of chromosome I and chromosome VIII

A 17 kb region from near the right end of chromosome I of Saccharomyces cerevisiae was isolated on recombinant lambda bacteriophages. This region contained the PHO11 gene which was located only 3.4 kb from the right end of the chromosome. We found that this region also was repeated approximately 13 kb from the end of the chromosome VIII DNA molecule. The chromosome VIII sequence appears to be a previously unnamed acid phosphatase gene that we propose to call PHO12. Thus, similar to the repeated SUC, MAL, X and Y' sequences, some members of the repeated acid phosphatase gene family also appear near the termini of yeast chromosomes.

Regulated phosphorylation and dephosphorylation of GAL4, a transcriptional activator

In yeast, galactose triggers a rapid GAL4-dependent induction of galactose/melibiose regulon (GAL/MEL) gene transcription, and glucose represses this activation. We discovered that alterations in the physical state of the GAL4 protein correlate with activation and repression of the GAL/MEL genes. Using Western immunoblot assay, we observe two electrophoretic forms of GAL4 protein-GAL4I and GAL4II-in noninduced cells. In the absence of glucose, the addition of galactose to such cells results in the rapid appearance of a third and slower-migrating form, GAL4III, which differs from at least GAL4I by phosphorylation. GAL80-deletion cells that constitutively transcribe galactose-responsive genes due to the lack of the GAL80 protein, an antagonist of the GAL4 protein, exhibit GAL4III without galactose addition. Addition of glucose, which results in rapid repression of galactose gene transcription, triggers a rapid elimination of GAL4III and an increase in GAL4II. Cycloheximide experiments provide evidence that the galactose- and glucose-triggered GAL4 protein mobility shifts are due to post-translational modification. GAL4III is labeled with [32P]phosphate in vivo; in vivo 35S-labeled GAL4III could be converted by phosphatase treatment in vitro to GAL4I. We present a model proposing that phosphorylation state changes in the GAL4 protein are key to modulating its activity.

Mitochondrial transformation in yeast by bombardment with microprojectiles

The genetic transformation of mitochondria and chloroplasts has been an intractable problem. The newly developed "biolistic" (biological ballistic) process was used to deliver DNA into yeast cells to stably transform their mitochondria. A nonreverting strain, which is respiratory deficient because of a deletion in the mitochondrial oxi3 gene, was bombarded with tungsten microprojectiles coated with DNA bearing sequences that could correct the oxi3 deletion. Respiratory-competent transformants were obtained in which the introduced oxi3 DNA is integrated at the homologous site in the mitochondrial genome. Organelle genomes can now be manipulated by molecular genetic techniques in the same way as nuclear genomes.

Expression of hepatitis B virus middle and large surface antigen genes in Saccharomyces cerevisiae

The hepatitis B virus genome carries the surface antigen (SAg) gene and an open reading frame that encodes two SAg-related polypeptides: SAg with a 55-amino-acid N-terminal extension polypeptide and SAg with a 174-amino-acid N-terminal extension polypeptide. These are termed middle S and large S, respectively. These polypeptides or their glycosylated derivatives have been detected in Dane particles, but their chemical and biological properties have remained largely unknown because of their limited availability. We attempted to produce these proteins in Saccharomyces cerevisiae by placing the coding regions under the control of the promoter of the yeast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. Yeast cells carrying middle S and large S coding sequences produced 33,000- and 42,000-dalton products, respectively, each of which reacted with anti-S antibody and bound to polymerized human serum albumin, in accordance with the known properties of pre-S proteins from particles in human sera (K. H. Heermann, U. Goldmann, W. Schwartz, T. Seyffarth, H. Baumgarten, and W. H. Gerlich, J. Virol. 52:396-402, 1984; A. Machida, S. Kishimoto, H. Ohnuma, K. Baba, Y. Ito, H. Miyamoto, G. Funatsu, K. Oda, S. Usuda, S. Togami, T. Nakamura, Y. Miyakawa, and M. Mayumi, Gastroenterology 86:910-918, 1984). The middle S polypeptide is glycosylated and can be assembled into particles whose size and density are similar to those of SAg. However, this polypeptide was highly susceptible to proteolytic degradation into 29,000- and 26,000-dalton polypeptides, of which only the former retained the binding activity to polymerized albumin. The large S polypeptides are nonglycosylated, relatively stable, and do not seem to assemble into particles by themselves.

Signal peptide specificity in posttranslational processing of the plant protein phaseolin in Saccharomyces cerevisiae

We linked the cDNA coding region for the bean storage protein phaseolin to the promoter and regulatory region of the Saccharomyces cerevisiae repressible acid phosphatase gene (PHO5) in multicopy expression plasmids. Yeast transformants containing these plasmids expressed phaseolin at levels up to 3% of the total soluble cellular protein. Phaseolin polypeptides in S. cerevisiae were glycosylated, and their molecular weights suggested that the signal peptide had been processed. We also constructed a series of plasmids in which the phaseolin signal-peptide-coding region was either removed or replaced with increasing amounts of the amino-terminal coding region for acid phosphatase. Phaseolin polypeptides with no signal peptide were not posttranslationally modified in S. cerevisiae. Partial or complete substitution of the phaseolin signal peptide with that from acid phosphatase dramatically inhibited both signal peptide processing and glycosylation, suggesting that some specific feature of the phaseolin signal amino acid sequence was required for these modifications to occur. Larger hybrid proteins that included approximately one-half of the acid phosphatase sequence linked to the amino terminus of the mature phaseolin polypeptide did undergo proteolytic processing and glycosylation. However, these polypeptides were cleaved at several sites that are not normally used in the unaltered acid phosphatase protein.

PHO5 upstream sequences confer phosphate control on the constitutive PHO3 gene

To identify the sequences involved in the regulation of the yeast acid phosphatase gene (PHO5) we constructed a series of hybrid promoters. Increasing lengths of 5'-flanking sequences of the PHO5 gene were placed in front of the TATA-box of constitutively expressed acid phosphatase gene (PHO3). The PHO5/PHO3 promoter constructions were used to replace the entire PHO5, PHO3 gene cluster on chromosome II. Depending on the length of PHO5 5'-flanking sequences present the PHO3 gene driven by the hybrid promoter could now be derepressed in response to inorganic phosphate (low Pi) exactly as the PHO5 wild type gene. A critical regulatory element was located between position -402 to -351 (upstream from ATG) and sequences further downstream (from -351 to -300) could increase transcriptional activation. The transcription levels of PHO3 were determined by northern blot analysis, under repressed (high Pi) and derepressed (low Pi) conditions which was paralleled by an increase in extra-cellular acid phosphatase activity. Fully regulated promoter hybrids showed a 40-fold induction of mRNA levels, comparable to wild type PHO5 promoter. Sl-nuclease protection experiments revealed that the PHO5 5'-flanking sequences, placed in front of PHO3, did not change the PHO3 transcription initiation site/s.

Molecular analysis of SNF2 and SNF5, genes required for expression of glucose-repressible genes in Saccharomyces cerevisiae

The SNF2 and SNF5 genes are required for derepression of SUC2 and other glucose-repressible genes of Saccharomyces cerevisiae in response to glucose deprivation. Previous genetic evidence suggested that SNF2 and SNF5 have functionally related roles. We cloned both genes by complementation and showed that the cloned DNA was tightly linked to the corresponding chromosomal locus. Both genes in multiple copy complemented only the cognate snf mutation. The SNF2 gene encodes a 5.7-kilobase RNA, and the SNF5 gene encodes a 3-kilobase RNA. Both RNAs contained poly(A) and were present in low abundance. Neither was regulated by glucose repression, and the level of SNF2 RNA was not dependent on SNF5 function or vice versa. Disruption of either gene at its chromosomal locus still allowed low-level derepression of secreted invertase activity, suggesting that these genes are required for high-level expression but are not directly involved in regulation. Further evidence was the finding that snf2 and snf5 mutants failed to derepress acid phosphatase, which is not regulated by glucose repression. The SNF2 and SNF5 functions were required for derepression of SUC2 mRNA.

Structure of the transcriptionally repressed phosphate-repressible acid phosphatase gene (PHO5) of Saccharomyces cerevisiae

We developed a high-copy-number plasmid system containing the entire structural and regulatory sequences of the phosphate-repressible acid phosphatase (PHO5) gene and the TRP1/ARS1 replicator sequences of the yeast Saccharomyces cerevisiae to investigate the mechanism of repression-derepression of transcription. The resulting plasmid was used to transform either wild-type cells or a number of strains which contain mutations in various trans-acting regulatory loci for the production of acid phosphatase. Results of analysis of mRNA levels isolated from the transformed strains grown under repressed or derepressed conditions suggested that normal transcriptional regulation of the gene persisted, although gene copy number was significantly increased. Analysis of changes in linking number (i.e., the number of negative supercoils) of the plasmid isolated under repressed and derepressed growth conditions revealed that the transcriptionally inactive plasmid contained approximately three more negative supercoils than the transcriptionally active plasmid. This difference in topological state was similarly seen in a plasmid containing a sequence-related acid phosphatase gene (PHO11) under the same regulatory control system, but it was not seen in plasmids isolated from some strains containing mutations which caused either fully constitutive or nonderepressible production of acid phosphatase. Finally, analysis of the nucleosome positioning along the inactive gene sequence revealed that an abnormally broad internucleosomal spacer is present in a region presumed to function in the regulation of transcription by the level of Pi in the growth media.