TUF factor binds to the upstream region of the pyruvate decarboxylase structural gene (PDC1) of Saccharomyces cerevisiae

Influence of single nitrogen compounds on growth and fermentation performance of Starmerella bacillaris and Saccharomyces cerevisiae during alcoholic fermentation

Nitrogen is among the essential nutriments that govern interactions between yeast species in the wine environment. A thorough knowledge of how these yeasts assimilate the nitrogen compounds of grape juice is an important prerequisite for a successful co- or sequential fermentation. In the present study, we investigated the efficiency of 18 nitrogen sources for sustaining the growth and fermentation of two Starm. bacillaris strains displaying metabolic properties, compared to the reference yeast S. cerevisiae The analysis of growth and fermentation parameters provided a comprehensive picture of Starm. bacillaris preferences with respect to nitrogen sources for sustained growth and fermentation. Important differences were observed in S. cerevisiae regarding rates, final population and CO₂ production. In particular, Lys and His supported substantial Starm. bacillaris growth and fermentation contrary to S. cerevisiae, while only 3 nitrogen sources, Arg, NH4⁺ and Ser, promoted S. cerevisiae growth more efficiently than that of Starm. bacillaris strains. Furthermore, Starm. bacillaris strains displayed a higher fermentative activity than S. cerevisiae during the first phase of culture with Gly or Thr, when the former species consumed solely fructose. Finally, no correlation has been shown between the ability of nitrogen sources to support growth and their fermentation efficiency. The specificities of Starm. bacillaris regarding nitrogen sources preferences are related to its genetic background, but further investigations are needed to elucidate the molecular mechanisms involved. These data are essential elements to be taken into account in order to make the best use of the potential of the two species.IMPORTANCE Mixed fermentations combining non-Saccharomyces and S. cerevisiae strains are increasingly implemented in the wine sector as they offer promising opportunities to diversify the flavour profile of end-products. However, competition for nutrients between species can cause fermentation problems, which is a severe hindrance to the development of these approaches. With the knowledge provided in this study on the nitrogen preferences of Starm. bacillaris, winemakers will be able to set up a nitrogen nutrition scheme adapted to the requirement of each species during mixed fermentation, through must supplementation with relevant nitrogen compounds. This will prevent nitrogen depletion or competition between yeasts for nitrogen sources, and consequently potential issues during fermentation. The data of this study highlight the importance of an appropriate nitrogen resource management during co- or sequential fermentation for fully exploiting the phenotypic potential of non-Saccharomyces yeasts.

Decoding telomere protein Rap1: Its telomeric and nontelomeric functions and potential implications in diabetic cardiomyopathy

Mammalian Rap1, the most conserved telomere-interacting protein, beyond its role within nucleus for the maintenance of telomeric functions, is also well known for its pleiotropic functions in various physiological and pathological conditions associated with metabolism, inflammation and oxidative stress. For all these, nowadays Rap1 is the subject of critical investigations aimed to unveil its molecular signaling pathways and to scrutinize the applicability of its modulation as a promising therapeutic strategy with clinical relevance. However, the underlying intimate mechanisms of Rap1 are not extensively studied, but any modulation of this protein level has been associated with pathologies like inflammation, oxidative stress and deregulated metabolism. This is considerably important in light of the recent discovery of Rap1 modulation in diseases like cancer and cardiac metabolic disorders. In this review, we focus on both the telomeric and nontelomeric functions of Rap1 and its modulation in various health risks, especially on the heart.

The Neurospora crassa cfp promoter drives a carbon source-dependent expression of transgenes in filamentous fungi

AIMS

The objective of the present study was to determine the potential of promoter sequences from the cfp gene of Neurospora crassa to drive the expression of transgenes in filamentous fungi.

METHODS AND RESULTS

Northern blot analyses showed that the mRNA levels of cfp were rapidly modified in response to either inducing or repressing culture conditions. The hygromycin phosphotransferase (hph) and S-adenosylmethionine synthetase (eth-1) genes were fused to a minimal cfp promoter fragment (Pcfp) and used as reporter genes. These constructs were highly expressed in transformant N. crassa strains grown in media containing glucose or sucrose and repressed in media containing ethanol or ethanol plus glucose. A gene fusion of the cfp promoter to the beta-glucuronidase gene (cfp-uidA) showed identical patterns of expression in the heterologous filamentous fungus Aspergillus nidulans.

CONCLUSIONS

Our results show that the levels of expression of the native cfp gene, as well as reporter genes driven by cfp promoter sequences, can be rapidly modified in response to different carbon sources. These modified levels of expression are maintained by continuous growth in the presence of the corresponding carbon source.

SIGNIFICANCE AND IMPACT OF THE STUDY

We propose that the cfp promoter can be used to control the expression of transgenes in filamentous fungi in a carbon source-dependent fashion.

In vivo analysis of functional regions within yeast Rap1p

We have analyzed the in vivo importance of different regions of Rap1p, a yeast transcriptional regulator and telomere binding protein. A yeast strain (SCR101) containing a regulatable RAP1 gene was used to test functional complementation by a range of Rap1p derivatives. These experiments demonstrated that the C terminus of the protein, containing the putative transcriptional activation domain and the regions involved in silencing and telomere function, is not absolutely essential for cell growth, a result confirmed by sporulation of a diploid strain containing a C terminal deletion derivative of RAP1. Northern analysis with cells that expressed Rap1p lacking the transcriptional activation domain revealed that this region is important for the expression of only a subset of Rap1p-activated genes. The one essential region within Rap1p is the DNA binding domain. We have investigated the possibility that this region has additional functions. It contains two Myb-like subdomains separated by a linker region. Individual point mutations in the linker region had no effect on Rap1p function, although deletion of the region abolished cell growth. The second Myb-like subdomain contains a large unstructured loop of unknown function. Domain swap experiments with combinations of elements from DNA binding domains of Rap1p homologues from different yeasts revealed that major changes can be made to the amino acid composition of this region without affecting Rap1p function.

Identification of a gene encoding the pyruvate decarboxylase gene regulator CaPdc2p from Candida albicans

In a screen for Candida albicans genes encoding transactivating proteins, a pyruvate decarboxylase (EC 4.1.1.1.) regulator gene was isolated. An open reading frame (ORF) of 2511 bp was identified encoding a predicted protein of 836 amino acids with a molecular weight of 94.4 kDa. The protein showed glutamine- and proline-rich stretches typical for transcriptional activators. The amino acid sequence comparisons between CaPdc2p of C. albicans and both Pdc2p of Saccharomyces cerevisiae and Rag3p of Kluyveromyces lactis, revealed similarities of 40% and 39%, respectively. The CaPDC2 gene was localized on chromosome 1. Southern blot analysis indicated that CaPDC2 might be a single copy gene. The growth defect of a S. cerevisiae pdc2 delta mutant on glucose was compensated by transformation of the C. albicans CaPDC2 gene.

Regulation of the expression of the Kluyveromyces lactis PDC1 gene: carbon source-responsive elements and autoregulation

The yeast Kluyveromyces lactis has a single structural gene coding for pyruvate decarboxylase (KIPDC1). In order to study the regulation of the expression of KIPDC1, we have sequenced (EMBL Accession No. Y15435) its promoter and have fused the promoter to the reporter gene lacZ from E. coli. Transcription analysis in a Klpdc1 delta strain showed that KIPDC1 expression is subject to autoregulation. The PDC1 gene from Saccharomyces cerevisiae was able to complement the Rag- phenotype of the Klpdc1 delta mutant strain and it could also repress transcription of the KIPDC1-lacZ fusion on glucose. A deletion analysis of the promoter region was performed to study carbon source-dependent regulation and revealed that at least two cis-acting regions are necessary for full induction of gene expression on glucose. Other cis-elements mediate repression on ethanol.

Multiple domains of repressor activator protein 1 contribute to facilitated binding of glycolysis regulatory protein 1

The function of repressor activator protein 1 (Rap1p) at glycolytic enzyme gene upstream activating sequence (UAS) elements in Saccharomyces cerevisiae is to facilitate binding of glycolysis regulatory protein 1 (Gcr1p) at adjacent sites. Rap1p has a modular domain structure. In its amino terminus there is an asymmetric DNA-bending domain, which is distinct from its DNA-binding domain, which resides in the middle of the protein. In the carboxyl terminus of Rap1p lie its silencing and putative activation domains. We carried out a molecular dissection of Rap1p to identify domains contributing to its ability to facilitate binding of Gcr1p. We prepared full-length and three truncated versions of Rap1p and tested their ability to facilitate binding of Gcr1p by gel shift assay. The ability to detect ternary complexes containing Rap1p.DNA. Gcr1p depended on the presence of binding sites for both proteins in the probe DNA. The DNA-binding domain of Rap1p, although competent to bind DNA, was unable to facilitate binding of Gcr1p. Full-length Rap1p and the amino- and carboxyl-truncated versions of Rap1p were each able to facilitate binding of Gcr1p at an appropriately spaced binding site. Under these conditions, Gcr1p displayed an approximately 4-fold greater affinity for Rap1p-bound DNA than for otherwise identical free DNA. When spacing between Rap1p- and Gcr1p-binding sites was altered by insertion of five nucleotides, the ability to form ternary Rap1p.DNA.Gcr1p complexes was inhibited by all but the DNA-binding domain of Rap1p itself; however, the ability of each individual protein to bind the DNA probe was unaffected.

Transient mRNA responses in chemostat cultures as a method of defining putative regulatory elements: application to genes involved in Saccharomyces cerevisiae acetyl-coenzyme A metabolism

To identify common regulatory sequences in the promoters of genes, transcription of 31 genes of Saccharomyces cerevisiae was analysed during the transient response to a glucose pulse in a chemostat culture. mRNA levels were monitored during the subsequent excess glucose, ethanol and acetate phases, while other conditions were kept constant. This setup allowed a direct comparison between regulation by glucose, ethanol and acetate. Genes with identical regulation patterns were grouped to identify regulatory elements in the promoters. In respect to regulation on glucose four classes were identified: no transcription under any of the conditions tested, no difference in regulation on glucose, induced on glucose and repressed on glucose. In addition, genes were found that were repressed or induced on ethanol or acetate. Sequence alignment of genes with similar regulation patterns revealed five new, putative regulatory promoter elements. (i) The glucose-inducible fermentation genes PDC1 and ADH1 share the sequence ATACCTTCSTT. (ii) Acetate-repression might be mediated by the decamer CCCGAG RGGA, present in the promoters of ACS2 and ACR1. (iii) A specific element (CCWTTSRNCCG) for the glyoxylate cycle was present in seven genes studied: CIT2, ICL1, MLS1, MDH2, CAT2, ACR1 and ACH1. These genes were derepressed on ethanol or acetate. (iv) The sequence ACGTSCRGAATGA was found in the promoters of the partially ethanol-repressed genes ACS1 and YAT1. (v) Ethanol induction, as seen for ACS2, ADH3 and MDH1, might be mediated via the sequence CGGSGCCGRAG.

Thiamin metabolism and thiamin diphosphate-dependent enzymes in the yeast Saccharomyces cerevisiae: genetic regulation

The yeast Saccharomyces cerevisiae utilises external thiamin for the production of thiamin diphosphate (ThDP) or can synthesise the cofactor itself. Prior to uptake into the cell thiamin phosphates are first hydrolysed and thiamin is taken up as free vitamin which is then pyrophosphorylated by a pyrophosphokinase. Synthesis of ThDP starts with the production of hydroxyethylthiazole and hydroxymethylpyrimidine. Those are linked to yield thiamin phosphate which is hydrolysed to thiamin and subsequently pyrophosphorylated. The THI genes encoding the enzymes of these final steps of ThDP production and of thiamin utilisation have been identified. Their expression is controlled by the level of thiamin and a number of regulatory proteins involved in regulated expression of the THI genes are known. However, the molecular details of the regulatory circuits need to be deciphered. Since the nucleotide sequence of the entire yeast genome is known we can predict the number of ThDP-dependent enzymes in S. cerevisiae. Eleven such proteins have been found: pyruvate decarboxylase (Pdc, three isoforms), acetolactate synthase, a putative alpha-ketoisocaproate decarboxylase with a regulatory role in ThDP synthesis and two proteins of unknown function form the group of Pdc related enzymes. In addition there are two isoforms for transketolase as well as the E1 subunits of pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase. Expression of most of these genes is either induced or repressed by glucose. Surprisingly, it has been found recently that expression of one of the genes for Pdc is repressed by thiamin. In addition, the regulatory protein Pdc2p was shown to be required for high level expression of both the THI and the PDC genes. Apparently, the production of ThDP and of the enzymes using this cofactor is coordinately regulated. Future research will focus on the elucidation of the molecular mechanisms of this novel type of regulation.

Suppression of pdc2 regulating pyruvate decarboxylase synthesis in yeast

Mutants lacking pyruvate decarboxylase cannot grow on glucose. We have isolated three different complementation groups of extragenic suppressors that suppress mutations in pdc2, a regulatory locus required for the synthesis of the glycolytic enzyme pyruvate decarboxylase. The most frequent of these is a recessive mutation in the structural gene PFK1 of the soluble phosphofructokinase. The other class XSP18 (extragenic suppressor of pdc2) is a dominant temperature-sensitive suppressor that allows the cells to grow on glucose only at 30 degrees but not at 36 degrees. It also affects the normal induction of the glucose-inducible enolase 2, which can be rescued by providing a copy of wild-type xsp18 in trans-heterozygotes. The pyruvate decarboxylase activity in the triple mutant pdc2 pfk1 XSP18 is nearly equal to the sum of the activities in the two double mutants pdc2 pfk1 and pdc2 XSP18, respectively. This implies that the two suppressors act through independent pathways or that there is no cooperativity between them. In the pdc2 pfk1 XSP18, strain, pfk1 suppresses the loss of induction of glucose-inducible enolase 2 brought about by XSP18 but fails to rescue temperature sensitivity. The third class (xsp37) supports the growth of the pdc2 mutant on glucose but fails to support growth on gluconeogenic carbon sources. All the three suppressors suppress pdc2 delta as well and act on PDC1 at the level of transcription.

ERA, a novel cis-acting element required for autoregulation and ethanol repression of PDC1 transcription in Saccharomyces cerevisiae

Yeast pyruvate decarboxylase (Pdc) catalyses the reaction at the branch-point of fermentation and respiration. In this work we have investigated the mechanisms of its transcriptional regulation in response to glucose and the non-fermentable carbon source ethanol. For this purpose we studied the function of different promoter fragments of PDC1, encoding the major pyruvate decarboxylase enzyme in wild-type cells, in the basal CYC1 promoter context. Thus, we identified a sequence mediating the response to ethanol and provide evidence showing that transcription of PDC1 is controlled by ethanol repression rather than by glucose induction. Furthermore, we showed that the same sequence is responsible for an autoregulatory process, leading to increased transcription from both the PDC1 and the PDC5 promoters, in strains in which the genomic copy of PDC1 is deleted. In addition, we have confirmed the role of Rap1 binding and have demonstrated that the Gcr1 protein also acts in transcriptional activation. DNA-protein interactions at the consensus Rap1-binding site and the newly identified ethanol-repression sequence (5'-AAATGCATA-3', termed 'ERA') were investigated by gel-shift and footprint analyses. Both DNA-binding activities were found in extracts from cells grown in media containing glucose or ethanol as the carbon source, indicating that the capacity to bind is not altered by the carbon source used.

Activation mechanism of the multifunctional transcription factor repressor-activator protein 1 (Rap1p)

Transcriptional activation in eukaryotic organisms normally requires combinatorial interactions of multiple transcription factors. In most cases, the precise role played by each transcription factor is not known. The upstream activating sequence (UAS) elements of glycolytic enzyme genes in Saccharomyces cerevisiae are excellent model systems for the study of combinatorial interactions. The yeast protein known as Rap1p acts as both a transcriptional repressor and an activator, depending on sequence context. Rap1p-binding sites are found adjacent to Gcr1p-binding sites in the UAS elements of glycolytic enzyme genes. These UAS elements constitute some of the strongest activating sequences known in S. cerevisiae. In this study, we have investigated the relationship between Rap1p- and Gcr1p-binding sites and the proteins that bind them. In vivo DNA-binding studies with rap1ts mutant strains demonstrated that the inability of Rap1p to bind at its site resulted in the inability of Gcr1p to bind at adjacent binding sites. Synthetic oligonucleotides, modeled on the UAS element of PYK1, in which the relative positions of the Rap1p- and Gcr1p-binding sites were varied prepared and tested for their ability to function as UAS elements. The ability of the oligonucleotides to function as UAS elements was dependent not only on the presence of both binding sites but also on the relative distance between the binding sites. In vivo DNA-binding studies showed that the ability of Rap1p bind its site was independent of Gcr1p but that the ability of Gcr1p to bind its site was dependent on the presence of an appropriately spaced and bound Rap1p-binding site. In vitro binding studies showed Rap1p-enhanced binding of Gcr1p on oligonucleotides modeled after the native PYK1 UAS element but not when the Rap1p- and Gcr1p-binding sites were displaced by 5 nucleotides. This work demonstrates that the role of the Rap1p in the activation of glycolytic enzyme genes is to bind in their UAS elements and to facilitate the binding of Gcr1p at adjacent binding sites.

The multifunctional transcription factors Abf1p, Rap1p and Reb1p are required for full transcriptional activation of the chromosomal PGK gene in Saccharomyces cerevisiae

We have identified two new transcription factor binding sites upstream of the previously defined UAS within the phosphoglycerate kinase (PGK) gene promoter in Saccharomyces cerevisiae. These sites are bound in vitro by the multifunctional factors Cpf1p and Reb1p. We have generated targeted deletions of Rap1p, Abf1p and Reb1p binding sites in the promoter of the chromosomal copy of the PGK gene. Northern blot analysis confirmed that most PGK promoter activity is mediated through the Rap1p binding site. However, significant effects are also mediated through both the Reb1p and Abf1p sites. In contrast, when the promoter is present on a high-copy-number plasmid, both the Abf1p and Reb1p sites play no role in transcriptional activation. The role of Cpf1p was examined using a cpf1 null strain. Cpf1p was found to have little if any, effect on activation of either the chromosomal or plasmid-borne PGK gene.

Characterisation of PDC2, a gene necessary for high level expression of pyruvate decarboxylase structural genes in Saccharomyces cerevisiae

The regulatory gene PDC2 was identified in a screen for mutations affecting pyruvate decarboxylase activity in yeast. I have cloned and sequenced this gene. The predicted protein of 925 amino acids has no homology to any sequence in the databases. However, the protein sequence is rich in asparagine and serine residues, as is often found for transcriptional regulators. The PDC2 deletion mutant exhibits a phenotype very similar to, but more severe than that of the point mutant: a strongly reduced pyruvate decarboxylase specific activity, slow, respiration-dependent growth on glucose, and accumulation of pyruvate. The activity of other glycolytic enzymes seems to be unaffected by the pdc2 delta mutation. Synthesis of pyruvate decarboxylase is regulated by PDC2 at the transcriptional level. Expression of the major structural gene for pyruvate decarboxylase, PDC1, is strongly reduced in pdc2 delta mutants. Transcription of the generally more weakly expressed PDC5 gene appears to be entirely abolished. However, glucose induction of pyruvate decarboxylase synthesis is unaffected. Thus, PDC2 is either important for a high basal level of PDC gene expression or it plays a positive role in the autoregulation that controls expression of PDC1 and PDC5.

Induction of pyruvate decarboxylase in glycolysis mutants of Saccharomyces cerevisiae correlates with the concentrations of three-carbon glycolytic metabolites

Pyruvate decarboxylase, PDCase, activity in wild-type yeast cells growing on ethanol is quite low but increases up to tenfold upon addition of glucose, less with galactose and only slightly with glycerol. PDCase levels in glycolysis mutant strains growing on ethanol or acetate were higher than in the wild-type strain. These levels correlated with the sum of the concentrations of three-carbon glycolytic metabolites. The highest accumulation was observed in a fructose bisphosphate aldolase deletion mutant concomitant with the highest PDCase activity ever observed under gluconeogenic conditions. Glucose addition induced an increase in PDCase activity in all mutants. However, the enzyme activities never reached wild-type level. On the other hand, the PDCase levels in the different mutants again correlated with the sum of the concentrations of the three-carbon glycolytic metabolites. This was interpreted to mean that full induction of PDCase activity requires the accumulation of hexose- and triosephosphates.

A complex regulatory element from the yeast gene ENO2 modulates GCR1-dependent transcriptional activation

The GCR1 gene product is required for maximal transcription of many yeast genes including genes encoding glycolytic enzymes. Transcription of the yeast enolase gene ENO2 is reduced 50-fold in strains carrying a gcr1 null mutation. cis-acting sequences that are sufficient for GCR1-dependent regulation of ENO2 expression were identified by using an enhancerless CYC1 promoter which is not normally dependent on GCR1 for expression. A 60-bp ENO2 sequence that was sufficient to provide high-level, GCR1-dependent transcriptional activation of the CYC1 promoter was identified. This 60-bp element could be subdivided into a 30-bp sequence containing a novel RAP1-binding site and a GCR1-binding site which did not activate CYC1 transcription and a 30-bp sequence containing a novel enhancer element that conferred moderate levels of GCR1-independent transcriptional activation. The 60-bp CGCR1-dependent upstream activator sequence is located immediately downstream from previously mapped overlapping binding sites for the regulatory proteins ABFI and RAP1. Evidence is presented that the overlapping ABFI- and RAP1-binding sites function together with sequences that bind GCR1 and RAP1 to stage transcriptional activation of ENO2 expression.

A complex regulatory element from the yeast gene ENO2 modulates GCR1-dependent transcriptional activation

The GCR1 gene product is required for maximal transcription of many yeast genes including genes encoding glycolytic enzymes. Transcription of the yeast enolase gene ENO2 is reduced 50-fold in strains carrying a gcr1 null mutation. cis-acting sequences that are sufficient for GCR1-dependent regulation of ENO2 expression were identified by using an enhancerless CYC1 promoter which is not normally dependent on GCR1 for expression. A 60-bp ENO2 sequence that was sufficient to provide high-level, GCR1-dependent transcriptional activation of the CYC1 promoter was identified. This 60-bp element could be subdivided into a 30-bp sequence containing a novel RAP1-binding site and a GCR1-binding site which did not activate CYC1 transcription and a 30-bp sequence containing a novel enhancer element that conferred moderate levels of GCR1-independent transcriptional activation. The 60-bp CGCR1-dependent upstream activator sequence is located immediately downstream from previously mapped overlapping binding sites for the regulatory proteins ABFI and RAP1. Evidence is presented that the overlapping ABFI- and RAP1-binding sites function together with sequences that bind GCR1 and RAP1 to stage transcriptional activation of ENO2 expression.

Transcriptional control of yeast phosphoglycerate mutase-encoding gene

Yeast genes encoding enzymes of the glycolytic pathway are highly expressed due to transcriptional control elements in their promoters. We provide data on such elements in the 5'-noncoding sequences of the Saccharomyces cerevisiae GPM1 gene, encoding phosphoglycerate mutase. Using fusions to the lacZ reporter gene, a detailed deletion analysis was performed. A palindromic sequence was shown to function as an upstream activation site (UAS) and two upstream repressing sites (URS1 and URS2) were located. Western and Northern blot analyses were used to substantiate the data obtained in enzymatic measurements. The regulatory sequences were shown to be functional in the heterologous CYC1 promoter. In addition, a promoter region was detected which mediated general glycolytic control by the GCR1 regulatory factor.

Concerted action of the transcriptional activators REB1, RAP1, and GCR1 in the high-level expression of the glycolytic gene TPI

In Saccharomyces cerevisiae, the TPI gene product, triosephosphate isomerase, makes up about 2% of the soluble cellular protein. Using in vitro and in vivo footprinting techniques, we have identified four binding sites for three factors in the 5' noncoding region of TPI: a REB1-binding site located at positions -401 to -392, two GCR1-binding sites located at positions -381 to -366 and -341 to -326, and a RAP1-binding site located at positions -358 to -346. We tested the effects of mutations at each of these binding sites on the expression of a TPI::lacZ gene fusion which carried 853 bp of the TPI 5' noncoding region integrated at the URA3 locus. The REB1-binding site is dispensable when material 5' to it is deleted; however, if the sequence 5' to the REB1-binding site is from the TPI locus, expression is reduced fivefold when the site is mutated. Because REB1 blocks nucleosome formation, the most likely function of its binding site in the TPI controlling region is to prevent the formation of nucleosomes over the TPI upstream activation sequence. Mutations in the RAP1-binding site resulted in a 10-fold reduction in expression of the reporter gene. Mutating either GCR1-binding site alone had a modest effect on expression of the fusion. However, mutating both GCR1-binding sites resulted in a 68-fold reduction in the level of expression of the reporter gene. A LexA-GCR1 fusion protein containing the DNA-binding domain of LexA fused to the amino terminus of GCR1 was able to activate expression of a lex operator::GAL1::lacZ reporter gene 116-fold over background levels. From this experiment, we conclude that GCR1 is able to activate gene expression in the absence of REB1 or RAP1 bound at adjacent binding sites. On the basis of these results, we suggest that GCR1 binding is required for activation of TPI and other GCR1-dependent genes and that the primary role of other factors which bind adjacent to GCR1-binding sites is to facilitate of modulate GCR1 binding in vivo.

Concerted action of the transcriptional activators REB1, RAP1, and GCR1 in the high-level expression of the glycolytic gene TPI

In Saccharomyces cerevisiae, the TPI gene product, triosephosphate isomerase, makes up about 2% of the soluble cellular protein. Using in vitro and in vivo footprinting techniques, we have identified four binding sites for three factors in the 5' noncoding region of TPI: a REB1-binding site located at positions -401 to -392, two GCR1-binding sites located at positions -381 to -366 and -341 to -326, and a RAP1-binding site located at positions -358 to -346. We tested the effects of mutations at each of these binding sites on the expression of a TPI::lacZ gene fusion which carried 853 bp of the TPI 5' noncoding region integrated at the URA3 locus. The REB1-binding site is dispensable when material 5' to it is deleted; however, if the sequence 5' to the REB1-binding site is from the TPI locus, expression is reduced fivefold when the site is mutated. Because REB1 blocks nucleosome formation, the most likely function of its binding site in the TPI controlling region is to prevent the formation of nucleosomes over the TPI upstream activation sequence. Mutations in the RAP1-binding site resulted in a 10-fold reduction in expression of the reporter gene. Mutating either GCR1-binding site alone had a modest effect on expression of the fusion. However, mutating both GCR1-binding sites resulted in a 68-fold reduction in the level of expression of the reporter gene. A LexA-GCR1 fusion protein containing the DNA-binding domain of LexA fused to the amino terminus of GCR1 was able to activate expression of a lex operator::GAL1::lacZ reporter gene 116-fold over background levels. From this experiment, we conclude that GCR1 is able to activate gene expression in the absence of REB1 or RAP1 bound at adjacent binding sites. On the basis of these results, we suggest that GCR1 binding is required for activation of TPI and other GCR1-dependent genes and that the primary role of other factors which bind adjacent to GCR1-binding sites is to facilitate of modulate GCR1 binding in vivo.

Characterization of the DNA-binding activity of GCR1: in vivo evidence for two GCR1-binding sites in the upstream activating sequence of TPI of Saccharomyces cerevisiae

GCR1 gene function is required for high-level glycolytic gene expression in Saccharomyces cerevisiae. Recently, we suggested that the CTTCC sequence motif found in front of many genes encoding glycolytic enzymes lay at the core of the GCR1-binding site. Here we mapped the DNA-binding domain of GCR1 to the carboxy-terminal 154 amino acids of the polypeptide. DNase I protection studies showed that a hybrid MBP-GCR1 fusion protein protected a region of the upstream activating sequence of TPI (UASTPI), which harbored the CTTCC sequence motif, and suggested that the fusion protein might also interact with a region of the UAS that contained the related sequence CATCC. A series of in vivo G methylation protection experiments of the native TPI promoter were carried out with wild-type and gcr1 deletion mutant strains. The G doublets that correspond to the C doublets in each site were protected in the wild-type strain but not in the gcr1 mutant strain. These data demonstrate that the UAS of TPI contains two GCR1-binding sites which are occupied in vivo. Furthermore, adjacent RAP1/GRF1/TUF- and REB1/GRF2/QBP/Y-binding sites in UASTPI were occupied in the backgrounds of both strains. In addition, DNA band-shift assays were used to show that the MBP-GCR1 fusion protein was able to form nucleoprotein complexes with oligonucleotides that contained CTTCC sequence elements found in front of other glycolytic genes, namely, PGK, ENO1, PYK, and ADH1, all of which are dependent on GCR1 gene function for full expression. However, we were unable to detect specific interactions with CTTCC sequence elements found in front of the translational component genes TEF1, TEF2, and CRY1. Taken together, these experiments have allowed us to propose a consensus GCR1-binding site which is 5'-(T/A)N(T/C)N(G/A)NC(T/A)TCC(T/A)N(T/A)(T/A)(T/G)-3'.

Characterization of the DNA-binding activity of GCR1: in vivo evidence for two GCR1-binding sites in the upstream activating sequence of TPI of Saccharomyces cerevisiae

GCR1 gene function is required for high-level glycolytic gene expression in Saccharomyces cerevisiae. Recently, we suggested that the CTTCC sequence motif found in front of many genes encoding glycolytic enzymes lay at the core of the GCR1-binding site. Here we mapped the DNA-binding domain of GCR1 to the carboxy-terminal 154 amino acids of the polypeptide. DNase I protection studies showed that a hybrid MBP-GCR1 fusion protein protected a region of the upstream activating sequence of TPI (UASTPI), which harbored the CTTCC sequence motif, and suggested that the fusion protein might also interact with a region of the UAS that contained the related sequence CATCC. A series of in vivo G methylation protection experiments of the native TPI promoter were carried out with wild-type and gcr1 deletion mutant strains. The G doublets that correspond to the C doublets in each site were protected in the wild-type strain but not in the gcr1 mutant strain. These data demonstrate that the UAS of TPI contains two GCR1-binding sites which are occupied in vivo. Furthermore, adjacent RAP1/GRF1/TUF- and REB1/GRF2/QBP/Y-binding sites in UASTPI were occupied in the backgrounds of both strains. In addition, DNA band-shift assays were used to show that the MBP-GCR1 fusion protein was able to form nucleoprotein complexes with oligonucleotides that contained CTTCC sequence elements found in front of other glycolytic genes, namely, PGK, ENO1, PYK, and ADH1, all of which are dependent on GCR1 gene function for full expression. However, we were unable to detect specific interactions with CTTCC sequence elements found in front of the translational component genes TEF1, TEF2, and CRY1. Taken together, these experiments have allowed us to propose a consensus GCR1-binding site which is 5'-(T/A)N(T/C)N(G/A)NC(T/A)TCC(T/A)N(T/A)(T/A)(T/G)-3'.

The promoter of Saccharomyces cerevisiae FBA1 gene contains a single positive upstream regulatory element

The glycolytic enzyme fructose 1,6-bisphosphate aldolase is encoded by the FBA1 gene of Saccharomyces cerevisiae. Transcription of aldolase gene is not regulated by glucose and high levels of expression have been observed also during growth on nonfermentable carbon source. A FBA1::lacZ gene fusion was constructed and a deletion analysis demonstrated the presence of a unique cis-acting positive upstream element (UAS) required for high levels of FBA1 expression. This element is located between positions -550 and -440 upstream of the aldolase open reading frame and it contains sequences known to constitute the binding sites for the multifunctional proteins RAP1 and ABFI and two TTCC motifs.

Transcriptional control of yeast phosphofructokinase gene expression

We here provide the complete nucleotide sequences of the 5'-non-coding regions of the yeast phosphofructokinase genes, PFK1 and PFK2. lacZ fusions of the PFK1 and PFK2 promoters were constructed and a deletion analysis was performed. In contrast to other glycolytic gene promoters, no strong regulatory elements could be found. However, we detected moderate UAS and URS functions. In general, the effects on expression upon deletion of these regions were more pronounced on media containing ethanol than on those containing glucose as carbon sources. Overexpression of either one of the PFK genes led to a decreased enzymatic activity in a wild-type background but did not affect transcription from the promoters.

Sequence and localization of the gene encoding yeast phosphoglycerate mutase

In this study we report on the complete nucleotide sequence of the yeast phosphoglycerate mutase gene (GPM1) and its essential 5' and 3' non-coding regions. The transcriptional start points were determined by S1-mapping and sequencing of a cDNA clone. Several sequences identified as important for transcriptional regulation in yeast promoters are present upstream of the transcription start point. 3' to the coding region we sequenced a composite repetitive element which, apparently, originated from a recombination between a delta- and a tau-element. Finally, we mapped the GPM1 gene 13 cM distal to fas1 on chromosome XI.