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

The 9aaTAD Is Exclusive Activation Domain in Gal4

The Gal4 protein is a well-known prototypic acidic activator that has multiple activation domains. We have previously identified a new activation domain called the nine amino acid transactivation domain (9aaTAD) in Gal4 protein. The family of the 9aaTAD activators currently comprises over 40 members including p53, MLL, E2A and other members of the Gal4 family; Oaf1, Pip2, Pdr1 and Pdr3. In this study, we revised function of all reported Gal4 activation domains. Surprisingly, we found that beside of the activation domain 9aaTAD none of the previously reported activation domains had considerable transactivation potential and were not involved in the activation of transcription. Our results demonstrated that the 9aaTAD domain is the only decisive activation domain in the Gal4 protein. We found that the artificial peptides included in the original Gal4 constructs were results of an unintended consequence of cloning that were responsible for the artificial transcriptional activity. Importantly, the activation domain 9aaTAD, which is the exclusive activation domain in Gal4, is also the central part of a conserved sequence recognized by the inhibitory protein Gal80. We propose a revision of the Gal4 regulation, in which the activation domain 9aaTAD is directly linked to both activation function and Gal80 mediated inhibition.

Identification of regulatory genes of riboflavin permease and α-glucosidase in the yeast Pichia guilliermondii

The method for a positive selection of Pichia guilliermondii yeast mutants which constitutively synthesize riboflavin (RF) permease has been developed. A genetic analysis revealed two regulatory genes of negative action (RFP80, RFP81) and one gene of positive action (RFP82); mutations in these loci determined the ability to synthesize RF permease in the medium without an inducer (α-glucosides). The constitutive mutants with cold-sensitive products of RFP80 and RFP81 genes were isolated. Interafelic complementation within RFP80 locus as well as restoration of the wild (inducible) phenotype in some hybrids between recessive rfp80 mutants and dominant RFP82 (c) mutants were observed. These data suggest a protein structure of products of identified regulatory loci and a direct interaction of the products of RFP80 and RFP82 genes.A meiotic segregants unable to synthesize RF permease in the inducer-containing media (genotype rfp82) were isolated by means of intragenic recombination in RFP82 locus. Epistasis-hypostasis test showed that gene RFP82 acted after gene RFP80. RFP80, RFP81 and RFP82 loci are involved in regulation of biosynthesis of both RF permease and α-glucosidase. The model for action of RFP80 and RFP82 gene products in the expression of RF permease and α-glucosidase structural genes of P. gulliermondii is presented.

The hydrophobic patch of ubiquitin is required to protect transactivator-promoter complexes from destabilization by the proteasomal ATPases

Mono-ubiquitylation of a transactivator is known to promote transcriptional activation of certain transactivator proteins. For the Sacchromyces cerevisiae transactivator, GAL4, attachment of mono-ubiquitin prevents destabilization of the DNA-transactivator complex by the ATPases of the 26S proteasome. This inhibition of destabilization depends on the arrangement of ubiquitin; a chain of ubiquitin tetramers linked through lysine 48 did not display the same protective effect as mono-ubiquitin. This led to an investigation into the properties of ubiquitin that may be responsible for this difference in activity between the different forms. We demonstrate the ubiquitin tetramers linked through lysine 63 do protect from proteasomal-mediated destabilization. In addition, we show that the mutating the isoleucine residue at position 44 interferes with proteasomal interaction in vitro and will abolish the protective activity in vivo. Together, these data implicate the hydrophobic patch of ubiquitin as required to protect transactivators from destabilization by the proteasomal ATPases.

Physical and functional interactions of monoubiquitylated transactivators with the proteasome

Destabilization of activator-DNA complexes by the proteasomal ATPases can inhibit transcription by limiting activator interaction with DNA. Modification of the activator by monoubiquitylation protects the activator from this destabilization activity. In this study, we probe the mechanism of this protective effect of monoubiquitylation. Using novel label transfer and chemical cross-linking techniques, we show that ubiquitin contacts the ATPase complex directly, apparently via Rpn1 and Rpt1. This interaction results in the dissociation of the activation domain-ATPase complex via an allosteric process. A model is proposed in which activator monoubiquitylation serves to limit the lifetime of the activator-ATPase complex interaction and thus the ability of the ATPases to unfold the activator and dissociate the protein-DNA complex.

Activation domain-dependent monoubiquitylation of Gal4 protein is essential for promoter binding in vivo

The Saccharomyces cerevisiae Gal4 protein is a paradigmatic transcriptional activator containing a C-terminal acidic activation domain (AD) of 34 amino acids. A mutation that results in the truncation of about two-thirds of the Gal4AD (gal4D) results in a crippled protein with only 3% the activity of the wild-type activator. We show here that although the Gal4D protein is not intrinsically deficient in DNA binding, it is nonetheless unable to stably occupy GAL promoters in vivo. This is because of the activity of the proteasomal ATPases, including Sug1/Rpt6, which bind to Gal4D via the remainder of the AD and strip it off of DNA. A mutation that suppressed the Gal4D "no growth on galactose" phenotype repressed the stripping activity of the ATPase complex but not other activities. We further demonstrate that Gal4D is hypersensitive to this stripping activity because of its failure to be monoubiquitylated efficiently in vivo and in vitro. Evidence is presented that the piece of the AD that is deleted in Gal4D protein is likely a recognition element for the E3 ubiquitin-protein ligase that modifies Gal4. These data argue that acidic ADs comprise at least two small peptide subdomains, one of which is responsible for activator monoubiquitylation and another that interacts with the proteasomal ATPases, coactivators and other transcription factors. This study validates the physiological importance of Gal4 monoubiquitylation and clarifies its major role as that of protecting the activator from being destabilized by the proteasomal ATPases.

Evidence that proteolysis of Gal4 cannot explain the transcriptional effects of proteasome ATPase mutations

The Gal system of Saccharomyces cerevisiae is a paradigm for eukaryotic gene regulation. Expression of genes required for growth on galactose is regulated by the transcriptional activator Gal4. The activation function of Gal4 has been localized to 34 amino acids near the C terminus of the protein. The gal4D allele of GAL4 encodes a truncated protein in which only 14 amino acids of the activation domain remain. Expression of GAL genes is dramatically reduced in gal4D strains and these strains are unable to grow on galactose as the sole carbon source. Overexpression of gal4D partially relieves the defect in GAL gene expression and allows growth on galactose. A search for extragenic suppressors of gal4D identified recessive mutations in the SUG1 and SUG2 genes, which encode ATPases of the 19S regulatory complex of the proteasome. The proteasome is responsible for the ATP-dependent degradation of proteins marked for destruction by the ubiquitin system. It has been commonly assumed that effects of SUG1 and SUG2 mutations on transcription are explained by alterations in the proteolysis of gal4D protein. We have investigated this assumption. Surprisingly, we find that SUG1 and SUG2 alleles that are unable to suppress gal4D cause a larger increase in gal4D protein levels than do suppressing alleles. In addition, mutations in genes encoding subunits of the proteolytic 20S sub-complex of the proteasome increase the levels of gal4D protein but do not rescue its transcriptional activity. Therefore, an alteration in the proteolysis of gal4D by the proteasome cannot explain the effects of mutations in SUG1 and SUG2 on expression of GAL genes. These findings suggest that the 19S regulatory complex may play a more direct role in transcription.

Yeast carbon catabolite repression

Glucose and related sugars repress the transcription of genes encoding enzymes required for the utilization of alternative carbon sources; some of these genes are also repressed by other sugars such as galactose, and the process is known as catabolite repression. The different sugars produce signals which modify the conformation of certain proteins that, in turn, directly or through a regulatory cascade affect the expression of the genes subject to catabolite repression. These genes are not all controlled by a single set of regulatory proteins, but there are different circuits of repression for different groups of genes. However, the protein kinase Snf1/Cat1 is shared by the various circuits and is therefore a central element in the regulatory process. Snf1 is not operative in the presence of glucose, and preliminary evidence suggests that Snf1 is in a dephosphorylated state under these conditions. However, the enzymes that phosphorylate and dephosphorylate Snf1 have not been identified, and it is not known how the presence of glucose may affect their activity. What has been established is that Snf1 remains active in mutants lacking either the proteins Grr1/Cat80 or Hxk2 or the Glc7 complex, which functions as a protein phosphatase. One of the main roles of Snf1 is to relieve repression by the Mig1 complex, but it is also required for the operation of transcription factors such as Adr1 and possibly other factors that are still unidentified. Although our knowledge of catabolite repression is still very incomplete, it is possible in certain cases to propose a partial model of the way in which the different elements involved in catabolite repression may be integrated.

Novel Gal3 proteins showing altered Gal80p binding cause constitutive transcription of Gal4p-activated genes in Saccharomyces cerevisiae

Gal4p-mediated activation of galactose gene expression in Saccharomyces cerevisiae normally requires both galactose and the activity of Gal3p. Recent evidence suggests that in cells exposed to galactose, Gal3p binds to and inhibits Ga180p, an inhibitor of the transcriptional activator Gal4p. Here, we report on the isolation and characterization of novel mutant forms of Gal3p that can induce Gal4p activity independently of galactose. Five mutant GAL3(c) alleles were isolated by using a selection demanding constitutive expression of a GAL1 promoter-driven HIS3 gene. This constitutive effect is not due to overproduction of Gal3p. The level of constitutive GAL gene expression in cells bearing different GAL3(c) alleles varies over more than a fourfold range and increases in response to galactose. Utilizing glutathione S-transferase-Gal3p fusions, we determined that the mutant Gal3p proteins show altered Gal80p-binding characteristics. The Gal3p mutant proteins differ in their requirements for galactose and ATP for their Gal80p-binding ability. The behavior of the novel Gal3p proteins provides strong support for a model wherein galactose causes an alteration in Gal3p that increases either its ability to bind to Gal80p or its access to Gal80p. With the Gal3p-Gal80p interaction being a critical step in the induction process, the Gal3p proteins constitute an important new reagent for studying the induction mechanism through both in vivo and in vitro methods.

Isolation and characterization of SUG2. A novel ATPase family component of the yeast 26 S proteasome

Using a genetic strategy designed to find proteins involved in the function of the Saccharomyces cerevisiae transcriptional activator GAL4, we isolated mutants in two genes which rescue a class of gal4 activation domain mutants. One of these genes, SUG1, encodes a member of a large family of putative ATPases, the Conserved ATPase containing Domain (CAD) proteins (also known as AAA proteins) that are involved in a wide variety of cellular functions. Subsequently, SUG1 was identified as a subunit of the 26 S proteasome. We have now cloned the gene defined by the second complementation group. SUG2 encodes an essential 49-kDa protein that is also a member of the CAD family and is 43% identical to SUG1. The mutation in sug2-1, like that in sug1-1, is found in the CAD near the highly conserved ATPase motif. We present biochemical and genetic evidence that SUG2 is associated in vivo with SUG1 and is a novel CAD protein subunit of the 26 S proteasome. With its highly conserved mammalian homologs, human p42 and ground squirrel CADp44, SUG2 defines a new class of proteasomal CAD proteins.

CADp44: a novel regulatory subunit of the 26S proteasome and the mammalian homolog of yeast Sug2p

We have identified a novel protein, CADp44, based on the analysis of cDNAs derived from the brainstem of the 13-lined ground squirrel, Spermophilus tridecemlineatus. CADp44 has an unmodified molecular mass of 44,178 Da and contains multiple functional domains, including a conserved ATPase domain (CAD) and a leucine zipper motif. We show that distinct regions of the CADp44 sequence are identical to a set of peptides prepared from a recently identified bovine protein, referred to as p42, which is found in the PA700 regulatory complex of the 26S proteasome (DeMartino et al., 1996). We also show that CADp44 is the functional homolog of the newly characterized Sug2 protein from the budding yeast, Saccharomyces cerevisiae (Russell et al., 1996). Consistent with its role as a component of the 26S proteasome, CADp44 mRNA is found in all ground squirrel tissues examined. Evolutionary relationships based on sequence analysis show that both CADp44 and yeast Sug2p are distinct from the other five CAD ATPases found in the PA700, and together comprise the sixth and newest CAD subunit of the regulatory complex of the 26S proteasome.

cDNA cloning of p42, a shared subunit of two proteasome regulatory proteins, reveals a novel member of the AAA protein family

We have employed cDNA cloning to deduce the complete primary structure of p42, a protein previously identified as a common subunit of two proteasome regulatory proteins: PA700, a 700000-Da multisubunit complex that binds to the proteasome and promotes the ATP-dependent degradation of ubiquitinated proteins, and modulator, a 250000-Da PA700-dependent proteasome activator. Computer analysis reveals that p42 is a novel member of a large protein family characterized by a conserved 200 amino acid domain which contains a consensus sequence for ATP binding. Five other members of this family, termed AAA proteins (ATPases associated with a variety of cellular activities) are also subunits of PA700. Gel filtration chromatography was employed to determine the qualitative and quantitative distribution of p42 in crude soluble lysates of bovine red blood cells. These studies demonstrated that p42 was found in two multi-protein complexes: the 26S proteasome (formed from the 20S proteasome and PA700) and the modulator. These results establish the identity of a new protein involved in the regulation of proteasome function and indicate that this protein is found in at least two different protein complexes.

A ubiquitin-protein ligase (E3) mutation of Saccharomyces cerevisiae suppressed by co-overexpression of two ubiquitin-specific processing proteases

To isolate mutations related to the ubiquitin system, I constructed a plasmid carrying the YUH1 and UBP1 genes (genes of ubiquitin-specific processing proteases) whose expressions were under the control of the galactose-inducible GAL1-GAL10 promoter. Cells of a strain carrying the plasmid were mutagenized with ethyl methanesulfonate. One mutant, which showed galactose-dependent growth at a high temperature (37 degrees C), was isolated from about 380,000 mutagenized colonies. The mutation responsible for galactose-dependent growth at 37 degrees C was a single nuclear recessive mutation designated as uby1-1. UBP1 and YUH1 as well as the GAL1-GAL10 promoter are required to suppress uby1-1. At the restrictive temperature, a uby1-1 mutant did not arrest at a specific phase of the cell cycle, but still lost viability. Even at the permissive temperature (30 degrees C), the uby1-1 mutant grew somewhat slowly and showed pleiotropic phenotypes including hypersensitivity to stresses such as cadmium and canavanine, and sporulation defects. The genomic DNA fragments in a single-copy plasmid which complemented uby1-1 were isolated. Chromosomal mapping, sequencing and subcloning analyses indicated that the gene complementing uby1-1 is RSP5, which encodes a ubiquitin-protein ligase (E3) homologous to E6-AP (E6 associated protein). Deletion, complementation and linkage analyses revealed that UBY1 and RSP5 are the same gene. Therefore, the E3 protein encoded by RSP5 (UBY1) is required for vegetative growth, sporulation and stress response. The present procedure using suppression by co-overexpression of two cloned genes will be useful to isolate mutations of related genes and to analyze biochemical pathways and gene-interactions.

Genetic evidence that an activation domain of GAL4 does not require acidity and may form a beta sheet

Regulation of gene expression in eukaryotes relies on intricate protein-protein interactions. Transcription of the galactose genes in yeast has been a productive model for this type of interaction. The positive activator in this system, GAL4, has a bifunctional C-terminus. It contains both a prototypic acidic activation domain and a region that binds the negative regulator, GAL80. We have taken advantage of this colocalization of functions to subject the region to a constrained mutagenesis analysis: one function was maintained, while the other one was altered. This analysis and the experiments it suggested have led us to two conclusions: first, the acidic amino acids are not, as commonly thought, required for activation; second, this region is not unstructured or alpha helical, but its function may require a beta sheet.

Alterations in a yeast protein resembling HIV Tat-binding protein relieve requirement for an acidic activation domain in GAL4

The acidic transcriptional activation motif functions in all eukaryotes, which suggests that it makes contact with some universal component of the transcriptional apparatus. Transcriptional activation by the yeast regulatory protein GAL4 requires an acidic region at its carboxyl terminus. Here we implement a selection scheme to determine whether GAL4 can still function when this C-terminal domain has been deleted. It can, when accompanied by a mutation in the SUG1 gene which is an essential gene in yeast. Analysis of mutant SUG1 in combination with various alleles of GAL4 indicates that SUG1 acts through a transcriptional pathway that depends on GAL4, but requires a region of GAL4 other than the C-terminal acidic activation domain. The predicted amino-acid sequence of SUG1 closely resembles that of two human proteins, TBP1 and MSS1, which modulate expression mediated by the human immunodeficiency virus tat gene.

Nondissociation of GAL4 and GAL80 in vivo after galactose induction

Transcription of galactose-inducible genes in yeast is regulated by interaction between the activator protein GAL4 and the negative regulatory protein GAL80. It has been suggested that GAL80 binds to and represses GAL4 under uninduced conditions and dissociates from GAL4 on induction. However, the possibility that GAL80 remains associated with GAL4 after induction has not been ruled out. Experiments to discriminate between these two models were performed and revealed that GAL80 stays bound after induction.

Genetic mapping and biochemical analysis of mutants in the maltose regulatory gene of the MAL1 locus of Saccharomyces cerevisiae

The MAL1 locus of Saccharomyces cerevisiae comprises three genes necessary for maltose utilization: a regulatory (MALR), a maltose transport (MALT) and a maltase gene (MALS). A fine structure genetic map of the MAL1R gene was constructed and the order of mutations was confirmed by plasmid-mediated chromosomal recombination. The mutations cluster non-randomly within the 5' half of the gene, where the putative DNA binding domain of the encoded protein is located. Only mutations mal1R-22 and MAL1R-72 map in the 3' terminal half of the gene; these mutations cause a different pattern of transcriptional regulation of plasmid-borne MAL6T genes. Experiments supporting a direct involvement of the MALR-encoded protein in carbon catabolite repression of MAL gene expression are reported.

The yeast heat shock transcription factor contains a transcriptional activation domain whose activity is repressed under nonshock conditions

Transcription of heat shock genes is induced by exposure of cells to elevated temperatures or other stress conditions. In yeast, it is thought that induction of transcription is mediated by conversion of a DNA-bound transcriptionally inactive form of the heat shock transcription factor (HSTF) to a DNA-bound transcriptionally active form. We have identified domains in HSTF involved in transcriptional activation and in repression of transcriptional activation at non-shock temperatures. We present evidence that a temperature-regulated transcriptional activation domain exists in HSTF and that this domain is essential for survival of yeast cells at heat shock temperatures. We propose a model for temperature-regulated transcriptional activation by a derepression mechanism.

GAL4 mutations that separate the transcriptional activation and GAL80-interactive functions of the yeast GAL4 protein

The carboxy-terminal 28 amino acids of the Saccharomyces cerevisiae transcriptional activator protein GAL4 execute two functions--transcriptional activation and interaction with the negative regulatory protein, GAL80. Here we demonstrate that these two functions are separable by single amino acid changes within this region. We determined the sequences of four GAL4C-mutations, and characterized the abilities of the encoded GAL4C proteins to activate transcription of the galactose/melibiose regulon in the presence of GAL80 and superrepressible GAL80S alleles. One of the GAL4C mutations can be compensated by a specific GAL80S mutation, resulting in a wild-type phenotype. These results support the idea that while the GAL4 activation function tolerates at least minor alterations in the GAL4 carboxyl terminus, the GAL80-interactive function is highly sequence-specific and sensitive even to single amino acid alterations. They also argue that the GAL80S mutations affect the affinity of GAL80 for GAL4, and not the ability of GAL80 to bind inducer.

Isolation of constitutive mutations affecting the proline utilization pathway in Saccharomyces cerevisiae and molecular analysis of the PUT3 transcriptional activator

The enzymes of the proline utilization pathway (the products of the PUT1 and PUT2 genes) in Saccharomyces cerevisiae are coordinately regulated by proline and the PUT3 transcriptional activator. To learn more about the control of this pathway, constitutive mutations in PUT3 as well as in other regulators were sought. A scheme using a gene fusion between PUT1 (S. cerevisiae proline oxidase) and galK (Escherichia coli galactokinase) was developed to select directly for constitutive mutations affecting the PUT1 promoter. These mutations were secondarily screened for their effects in trans on the promoter of the PUT2 (delta 1-pyrroline-5-carboxylate dehydrogenase) gene by using a PUT2-lacZ (E. coli beta-galactosidase) gene fusion. Three different classes of mutations were isolated. The major class consisted of semidominant constitutive PUT3 mutations that caused PUT2-lacZ expression to vary from 2 to 22 times the uninduced level. A single dominant mutation in a new locus called PUT5 resulted in low-level constitutive expression of PUT2-lacZ; this mutation was epistatic to the recessive, noninducible put3-75 allele. Recessive constitutive mutations were isolated that had pleiotropic growth defects; it is possible that these mutations are not specific to the proline utilization pathway but may be in genes that control several pathways. Since the PUT3 gene appears to have a major role in the regulation of this pathway, a molecular analysis was undertaken. This gene was cloned by functional complementation of the put3-75 mutation. Strains carrying a complete deletion of this gene are viable, proline nonutilizing, and indistinguishable in phenotype from the original put3-75 allele. The PUT3 gene encodes a 2.8-kilobase-pair transcript that is not regulated by proline at the level of RNA accumulation. The presence of the gene on a high-copy-number plasmid did not alter the regulation of one of its target genes, PUT2-lacZ, suggesting that the PUT3 gene product is not limiting and that a titratable repressor is not involved in the regulation of this pathway.

Two new loci that give rise to dominant omnipotent suppressors in Saccharomyces cerevisiae

Ten dominant omnipotent suppressors of Saccharomyces cerevisiae, which were previously shown to be different from SUP46, have been examined. Nine are mapped in a region between lys5 and cyh2 on the left arm of chromosome VII. These suppressors, like SUP46, manifest sensitivity to increased temperature and the antibiotics paromomycin and hygromycin B. In addition, they have an identical action spectrum. These results strongly suggest that they are allelic to each other and they are designated SUP138. The tenth is mapped to a position between his1 and arg6 on the right arm of chromosome V. This suppressor, named SUP139, does not manifest temperature sensitivity nor antibiotic sensitivity. SUP139 and SUP138, which are clearly distinguished by means of action spectrum, act on much fewer nonsense mutations than SUP46. It is now clear that dominant omnipotent suppressors arising at a single locus are homogeneous and that their efficiency is locus-dependent. The order of efficiency is SUP46 greater than SUP138 greater than SUP139.

Isolation of constitutive mutations affecting the proline utilization pathway in Saccharomyces cerevisiae and molecular analysis of the PUT3 transcriptional activator

The enzymes of the proline utilization pathway (the products of the PUT1 and PUT2 genes) in Saccharomyces cerevisiae are coordinately regulated by proline and the PUT3 transcriptional activator. To learn more about the control of this pathway, constitutive mutations in PUT3 as well as in other regulators were sought. A scheme using a gene fusion between PUT1 (S. cerevisiae proline oxidase) and galK (Escherichia coli galactokinase) was developed to select directly for constitutive mutations affecting the PUT1 promoter. These mutations were secondarily screened for their effects in trans on the promoter of the PUT2 (delta 1-pyrroline-5-carboxylate dehydrogenase) gene by using a PUT2-lacZ (E. coli beta-galactosidase) gene fusion. Three different classes of mutations were isolated. The major class consisted of semidominant constitutive PUT3 mutations that caused PUT2-lacZ expression to vary from 2 to 22 times the uninduced level. A single dominant mutation in a new locus called PUT5 resulted in low-level constitutive expression of PUT2-lacZ; this mutation was epistatic to the recessive, noninducible put3-75 allele. Recessive constitutive mutations were isolated that had pleiotropic growth defects; it is possible that these mutations are not specific to the proline utilization pathway but may be in genes that control several pathways. Since the PUT3 gene appears to have a major role in the regulation of this pathway, a molecular analysis was undertaken. This gene was cloned by functional complementation of the put3-75 mutation. Strains carrying a complete deletion of this gene are viable, proline nonutilizing, and indistinguishable in phenotype from the original put3-75 allele. The PUT3 gene encodes a 2.8-kilobase-pair transcript that is not regulated by proline at the level of RNA accumulation. The presence of the gene on a high-copy-number plasmid did not alter the regulation of one of its target genes, PUT2-lacZ, suggesting that the PUT3 gene product is not limiting and that a titratable repressor is not involved in the regulation of this pathway.

A gene product needed for induction of allantoin system genes in Saccharomyces cerevisiae but not for their transcriptional activation

The allantoin-degradative pathway of Saccharomyces cerevisiae consists of several genes whose expression is highly induced by the presence of allophanic acid. Induced expression requires a functional DAL81 gene product. Analysis of these genes has demonstrated the presence of three cis-acting elements in the upstream regions: (i) an upstream activation sequence (UAS) required for transcriptional activation in an inducer-independent fashion, (ii) an upstream repression sequence (URS) that mediates inhibition of this transcriptional activation, and (iii) an upstream induction sequence (UIS) needed for a response to inducer. The UIS element mediates inhibition of URS-mediated function when inducer is present. We cloned and characterized the DAL81 gene and identified the element with which it was associated. The gene was found to encode a rare 3.2-kilobase-pair mRNA. The amount of DAL81-specific RNA responded neither to induction nor to nitrogen catabolite repression. Deletion of the DAL81 gene resulted in loss of induction but did not significantly affect basal level expression of the DAL7 and DUR1,2 genes or the UAS and URS functions present in plasmid constructions. These data suggest that (i) transcriptional activation of the DAL genes and their responses to inducer are mediated by different factors and cis-acting sequences and (ii) the UIS functions only when a wild-type DAL81 gene product is available.

A gene product needed for induction of allantoin system genes in Saccharomyces cerevisiae but not for their transcriptional activation

The allantoin-degradative pathway of Saccharomyces cerevisiae consists of several genes whose expression is highly induced by the presence of allophanic acid. Induced expression requires a functional DAL81 gene product. Analysis of these genes has demonstrated the presence of three cis-acting elements in the upstream regions: (i) an upstream activation sequence (UAS) required for transcriptional activation in an inducer-independent fashion, (ii) an upstream repression sequence (URS) that mediates inhibition of this transcriptional activation, and (iii) an upstream induction sequence (UIS) needed for a response to inducer. The UIS element mediates inhibition of URS-mediated function when inducer is present. We cloned and characterized the DAL81 gene and identified the element with which it was associated. The gene was found to encode a rare 3.2-kilobase-pair mRNA. The amount of DAL81-specific RNA responded neither to induction nor to nitrogen catabolite repression. Deletion of the DAL81 gene resulted in loss of induction but did not significantly affect basal level expression of the DAL7 and DUR1,2 genes or the UAS and URS functions present in plasmid constructions. These data suggest that (i) transcriptional activation of the DAL genes and their responses to inducer are mediated by different factors and cis-acting sequences and (ii) the UIS functions only when a wild-type DAL81 gene product is available.

Positive and negative regulatory elements control the expression of the UGA4 gene coding for the inducible 4-aminobutyric-acid-specific permease in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the pathway of 4-aminobutyric acid catabolism, for use as a nitrogen source, involves a specific permease (encoded by the UGA4 gene) and two enzymes (encoded by the UGA1 and UGA2 genes, respectively). The synthesis of these proteins is induced by 4-aminobutyrate. It also requires the product of the UGA3 gene. Here, we describe four additional regulatory mutations which provide evidence for the existence of both positive and negative regulatory elements which control the final expression of the UGA4 gene. Some of them simultaneously control the expression of the UGA1 and UGA2 genes. Three classes of mutant with a constitutive 4-aminobutyrate-specific permease have been isolated. (a) Recessive mutations in the UGA43 gene suggest that the product of the UGA43 gene behaves like a trans-acting negative regulator of UGA4 gene expression. (b) The semi-dominant mutation (uga11), closely linked to the UGA4 gene, might affect the receptor of the UGA43 gene product. In these two classes of mutant, only the permease is constitutive. (3) The uga81 mutation, closely linked to the UGA3 gene, makes the whole UGA regulon constitutive. On the other hand, recessive mutations at the UGA35 gene locus lead to non-inducibility of the UGA regulon. Hence the UGA35 gene product behaves like a second trans-acting positive regulator in addition to UGA3.

Functional homology between the yeast regulatory proteins GAL4 and LAC9: LAC9-mediated transcriptional activation in Kluyveromyces lactis involves protein binding to a regulatory sequence homologous to the GAL4 protein-binding site

As shown previously, the beta-galactosidase gene of Kluyveromyces lactis is transcriptionally regulated via an upstream activation site (UASL) which contains a sequence homologous to the GAL4 protein-binding site in Saccharomyces cerevisiae (M. Ruzzi, K.D. Breunig, A.G. Ficca, and C.P. Hollenberg, Mol. Cell. Biol. 7:991-997, 1987). Here we demonstrate that the region of homology specifically binds a K. lactis regulatory protein. The binding activity was detectable in protein extracts from wild-type cells enriched for DNA-binding proteins by heparin affinity chromatography. These extracts could be used directly for DNase I and exonuclease III protection experiments. A lac9 deletion strain, which fails to induce the beta-galactosidase gene, did not contain the binding factor. The homology of LAC9 protein with GAL4 (J.M. Salmeron and S. A. Johnston, Nucleic Acids Res. 14:7767-7781, 1986) strongly suggests that LAC9 protein binds directly to UASL and plays a role similar to that of GAL4 in regulating transcription.

Isolation and characterization of dominant mutations resistant to carbon catabolite repression of galactokinase synthesis in Saccharomyces cerevisiae

Seven dominant mutations showing greatly enhanced resistance to the glucose repression of galactokinase synthesis have been isolated from GAL81 mutants, which have the constitutive phenotype but are still strongly repressible by glucose for the synthesis of the Leloir enzymes. These glucose-resistant mutants were due to semidominant mutations at either of two loci, GAL82 and GAL83. Both loci are unlinked to the GAL81- gal4, gal80, or gal7 X gal10 X gal1 locus or to each other. The GAL83 locus was mapped on chromosome V at a site between arg9 and cho1. The GAL82 and GAL83 mutations produced partial resistance of galactokinase to glucose repression only when one or both of these mutations were combined with a GAL81 or a gal80 mutation. The GAL82 and GAL83 mutations are probably specific for expression of the Leloir pathway and related enzymes, because they do not affect the synthesis of alpha-D-glucosidase, invertase, or isocitrate lyase.

GAL1-GAL10 divergent promoter region of Saccharomyces cerevisiae contains negative control elements in addition to functionally separate and possibly overlapping upstream activating sequences

The upstream activating sequence (UASG) of the adjacent and divergently transcribed GAL1 and GAL10 promoters of Saccharomyces cerevisiae regulates the induction of the corresponding genes in response to the presence of galactose. We constructed chimeric yeast promoters in which a different UAS, UASC from the iso-1-cytochrome c (CYC1) gene of S. cerevisiae, was fused at different locations upstream of GAL1 (UASC-GAL1 promoters) or GAL10 (UASC-GAL10 promoters) and used to monitor the activity of UASG in cells grown in the presence or absence of galactose. Though the CYC1 promoter is fully induced in yeast grown in glycerol medium, UASC-GAL chimeric promoters containing UASG were repressed as much as 400-fold (UASC-GAL1) or 1350-fold (UASC-GAL10) in this growth medium. Several distinct portions of the GAL1-GAL10 divergent promoter region blocked the UASC-induced expression of the GAL1 and GAL10 promoters, whereas others did not, suggesting that several distinct negative control elements are present that may repress transcription of GAL1 and GAL10 in the absence of galactose. The approximate locations of these negative control elements were delimited to sites adjacent to or possibly overlapping the sites at which the positive control protein GAL4 binds in UASG. Deletion derivatives of GAL4 that fail to induce transcription from the wild-type GAL promoters but retain the DNA binding domain significantly derepressed the expression of the UASC-GAL chimeric promoters. These results, combined with those of earlier studies, suggest the possibility that GAL4 normally induces transcription of GAL1 and GAL10 by blocking the activity of these negative control elements, in addition to stimulating transcription by a mechanism of positive control.

Functional homology between the yeast regulatory proteins GAL4 and LAC9: LAC9-mediated transcriptional activation in Kluyveromyces lactis involves protein binding to a regulatory sequence homologous to the GAL4 protein-binding site

As shown previously, the beta-galactosidase gene of Kluyveromyces lactis is transcriptionally regulated via an upstream activation site (UASL) which contains a sequence homologous to the GAL4 protein-binding site in Saccharomyces cerevisiae (M. Ruzzi, K.D. Breunig, A.G. Ficca, and C.P. Hollenberg, Mol. Cell. Biol. 7:991-997, 1987). Here we demonstrate that the region of homology specifically binds a K. lactis regulatory protein. The binding activity was detectable in protein extracts from wild-type cells enriched for DNA-binding proteins by heparin affinity chromatography. These extracts could be used directly for DNase I and exonuclease III protection experiments. A lac9 deletion strain, which fails to induce the beta-galactosidase gene, did not contain the binding factor. The homology of LAC9 protein with GAL4 (J.M. Salmeron and S. A. Johnston, Nucleic Acids Res. 14:7767-7781, 1986) strongly suggests that LAC9 protein binds directly to UASL and plays a role similar to that of GAL4 in regulating transcription.

The carboxy-terminal 30 amino acids of GAL4 are recognized by GAL80

In wild-type yeast the action of the transcriptional activator GAL4 is inhibited by GAL80, and galactose relieves this inhibition. We show that deletion mutants of GAL4 lacking 30 amino acids of the carboxyl terminus activate transcription constitutively, whereas other deletion mutants bearing the carboxy-terminal 30 amino acids are inhibited by GAL80. Moreover, GAL4 fragments bearing these 30 amino acids, when expressed from a strong promoter on multicopy plasmids, free the endogenous GAL4 from inhibition by GAL80. These and other results suggest that GAL80 recognizes the carboxy-terminal 30 amino acids of GAL4, forming a complex that, though bound to DNA, does not activate transcription.

Interaction of positive and negative regulatory proteins in the galactose regulon of yeast

Transcriptional regulation in the galactose regulon of yeast is determined by an interplay between a positive regulatory protein, GAL4, and a negative regulatory protein, GAL80. We show that derivatives of GAL4 missing as few as 28 carboxy-terminal amino acids are not responsive to GAL80 regulation, implying that the carboxyl terminus of GAL4 is required for interaction with GAL80. Furthermore, a lesion in GAL4 that genetically defines the GAL80-interactive region maps to the 3' end of the gene. Since the carboxyl terminus of GAL4 has also been implicated in interaction with a transcriptional factor, we propose a model for negative regulation in which GAL80 and this factor compete for binding a common region of GAL4, and the on/off state of transcription is determined by the relative affinities of the negative regulator and the transcriptional factor for this region.

Positive regulation of the beta-galactosidase gene from Kluyveromyces lactis is mediated by an upstream activation site that shows homology to the GAL upstream activation site of Saccharomyces cerevisiae

In contrast to the Escherichia coli lac operon, the yeast beta-galactosidase gene is positively regulated. In the 5'-noncoding region of the Kluyveromyces lactis LAC4 gene, we mapped an upstream activation site (UAS) that is required for induction. This sequence, located between positions -435 and -326 from the start of translation, functions irrespective of its orientation and can confer lactose regulation to the heterologous CYC1 promoter. It is composed of at least two subsequences that must act in concert. One of these subsequences showed a strong homology to the UAS consensus sequence of the Saccharomyces cerevisiae GAL genes (E. Giniger, S. M. Varnum, and M. Ptashne, Cell 40:767-774, 1985). We propose that this region of homology located at about position -426 is a binding site for the product of the regulatory gene LAC9 which probably induces transcription of the LAC4 gene in a manner analogous to that of the GAL4 protein.

Characterization of a positive regulatory gene, LAC9, that controls induction of the lactose-galactose regulon of Kluyveromyces lactis: structural and functional relationships to GAL4 of Saccharomyces cerevisiae

Lactose or galactose induces the expression of the lactose-galactose regulon in Kluyveromyces lactis. We show here that the regulon is not induced in strains defective in LAC9. We demonstrate that this gene codes for a regulatory protein that acts in a positive manner to induce transcription. The LAC9 gene was isolated by complementation of a lac9 defective strain. DNA sequence analysis of the gene gave a deduced protein of 865 amino acids. Comparison of this sequence with that of the GAL4 protein of Saccharomyces cerevisiae revealed three regions of homology. One region of about 90 amino acid occurs at the amino terminus, which is known to mediate binding of GAL4 protein to upstream activator sequences. We speculate that a portion of this region, adjacent to the "metal-binding finger," specifies DNA binding. We discuss possible functions of the two other regions of homology. The functional implications of these structural similarities were examined. When LAC9 was introduced into a gal4 defective strain of S. cerevisiae it complemented the mutation and activated the galactose-melibiose regulon. However, LAC9 did not simply mimic GAL4. Unlike normal S. cerevisiae carrying GAL4, the strain carrying LAC9 gave constitutive expression of GAL1 and MEL1, two genes in the regulon. The strain did show glucose repression of the regulon, but repression was less severe with LAC9 than with GAL4. We discuss the implications of these results and how they may facilitate our understanding of the LAC9 and GAL4 regulatory proteins.

The constitutive, glucose-repression-insensitive mutation of the yeast MAL4 locus is an alteration of the MAL43 gene

Mutations resulting in constitutive production of maltase have been identified at each of the five MAL loci of Saccharomyces yeasts. Here we examine a dominant constitutive, glucose-repression-insensitive allele of the MAL4 locus (MAL4-C). Our results demonstrate that MAL4-C is an alteration in the MAL43 gene, which encodes the positive regulator of the MAL structural genes, and that its product is trans-acting. The MAL43 gene from the MAL4-C strain was cloned and integrated into a series of nonfermenting strains lacking a functional regulatory gene but carrying copies of the maltose permease and maltase structural genes. Expression of the maltase structural gene was both constitutive and insensitive to glucose repression in these transformants. The MAL4-C allele also results in constitutive expression of the unlinked MAL12 gene (encoding maltase) in this strain. In addition, the cloned MAL43 gene was shown to be dominant to the wild-type MAL63 gene. We also show that most of the glucose repression insensitivity of strains carrying the MAL4-C allele results from alteration of MAL43.

Characterization of a positive regulatory gene, LAC9, that controls induction of the lactose-galactose regulon of Kluyveromyces lactis: structural and functional relationships to GAL4 of Saccharomyces cerevisiae

Lactose or galactose induces the expression of the lactose-galactose regulon in Kluyveromyces lactis. We show here that the regulon is not induced in strains defective in LAC9. We demonstrate that this gene codes for a regulatory protein that acts in a positive manner to induce transcription. The LAC9 gene was isolated by complementation of a lac9 defective strain. DNA sequence analysis of the gene gave a deduced protein of 865 amino acids. Comparison of this sequence with that of the GAL4 protein of Saccharomyces cerevisiae revealed three regions of homology. One region of about 90 amino acid occurs at the amino terminus, which is known to mediate binding of GAL4 protein to upstream activator sequences. We speculate that a portion of this region, adjacent to the "metal-binding finger," specifies DNA binding. We discuss possible functions of the two other regions of homology. The functional implications of these structural similarities were examined. When LAC9 was introduced into a gal4 defective strain of S. cerevisiae it complemented the mutation and activated the galactose-melibiose regulon. However, LAC9 did not simply mimic GAL4. Unlike normal S. cerevisiae carrying GAL4, the strain carrying LAC9 gave constitutive expression of GAL1 and MEL1, two genes in the regulon. The strain did show glucose repression of the regulon, but repression was less severe with LAC9 than with GAL4. We discuss the implications of these results and how they may facilitate our understanding of the LAC9 and GAL4 regulatory proteins.

Positive regulation of the beta-galactosidase gene from Kluyveromyces lactis is mediated by an upstream activation site that shows homology to the GAL upstream activation site of Saccharomyces cerevisiae

In contrast to the Escherichia coli lac operon, the yeast beta-galactosidase gene is positively regulated. In the 5'-noncoding region of the Kluyveromyces lactis LAC4 gene, we mapped an upstream activation site (UAS) that is required for induction. This sequence, located between positions -435 and -326 from the start of translation, functions irrespective of its orientation and can confer lactose regulation to the heterologous CYC1 promoter. It is composed of at least two subsequences that must act in concert. One of these subsequences showed a strong homology to the UAS consensus sequence of the Saccharomyces cerevisiae GAL genes (E. Giniger, S. M. Varnum, and M. Ptashne, Cell 40:767-774, 1985). We propose that this region of homology located at about position -426 is a binding site for the product of the regulatory gene LAC9 which probably induces transcription of the LAC4 gene in a manner analogous to that of the GAL4 protein.

Duplicate upstream activating sequences in the promoter region of the Saccharomyces cerevisiae GAL7 gene

We constructed a series of deletions in the 5' noncoding region of the Saccharomyces cerevisiae GAL7 gene, fused them to the Escherichia coli gene lacZ, and introduced them into yeasts by using a multicopy vector. We then studied the effect of the deletions on beta-galactosidase synthesis directed by the gene fusions in media with various carbon sources. This analysis identified a TATA box and two upstream activating sequences as necessary elements for galactose-controlled GAL7 transcription. Two upstream activating sequences exhibiting 71% homology with each other were located 255 and 168 base pairs, respectively, upstream of the GAL7 transcription start point. Each sequence consists of 21 base pairs, displaying an approximate rotational symmetry with a core consensus sequence of GAA--AGCTGCTTC--CGCG. At least one of the two sequences is required for galactose induction and also for glucose repression of the GAL7'-lac'Z gene. Analysis with host regulatory mutants delta gal14 and delta gal180 suggests that these sequences are the site at which the GAL4 product exerts its action to activate the GAL7 gene. We also observed that a deletion lacking both upstream activation sequences allowed the gene fusion to be expressed in the absence of galactose at about 10% of the fully induced level of the intact fusion. This constitutive expression depended on the presence of the TATA box of GAL7 in cis but not on a functional GAL4 gene. The level of the uncontrolled expression was decreased by increasing the distance between the TATA box and the pBR322 sequence in the vector plasmid.

Fluphenazine-resistant Saccharomyces cerevisiae mutants defective in the cell division cycle

An fls1 mutant of Saccharomyces cerevisiae, which did not grow in the presence of 30 micrograms of fluphenazine per ml, was isolated. Mutants that were resistant to 90 micrograms of fluphenazine per ml and temperature sensitive for growth were obtained from the fls1 mutant. One fluphenazine-resistance mutation, fsr1, was located near the his7 locus on chromosome II. Growth of the fsr1 mutants at 35 degrees C was arrested after nuclear division. The other group of fluphenazine-resistant mutants, carrying fsr2 mutations, showed Ca2+-dependent growth at 35 degrees C. Growth of the fsr2 mutants at 35 degrees C was arrested at the G2 stage of the cell cycle in Ca2+-poor medium.

Analysis of the Kluyveromyces lactis positive regulatory gene LAC9 reveals functional homology to, but sequence divergence from, the Saccharomyces cerevisiae GAL4 gene

The galactose metabolism positive regulatory gene from Kluyveromyces lactis, LAC9, has been isolated through its ability to activate expression of galactose metabolism enzyme genes in Saccharomyces cerevisiae. The LAC9 gene also activates expression of the S. cerevisiae alpha-galactosidase (MEL1) and K. lactis beta-galactosidase (LAC4) genes in S. cerevisiae. Although LAC9-activated gene expression in K. lactis is not glucose repressed, activation of MEL1 gene expression by LAC9 in S. cerevisiae is. The LAC9 gene is expressed at an extremely low level as a approximately 2.9-kb mRNA, and encodes a protein of 865 amino acids. Although the LAC9 gene is functionally analogous to the S. cerevisiae GAL4 gene, the bulk of its protein sequence shows little homology to that of GAL4. Two of the three regions of homology that do exist, however, are restricted to areas of GAL4 protein already implicated in nuclear localization, DNA binding, and transcriptional activation.

Autogenous regulation of the positive regulatory qa-1F gene in Neurospora crassa

In Neurospora crassa, the qa-1F regulatory gene positively controls transcription of all genes in the quinic acid (qa) gene cluster. qa-1F is transcribed at a low, uninduced level but is subject to strong (50-fold), autogenous regulation as well as to control by the negative regulatory gene, qa-1S, and the inducer quinic acid. Cloned qa-1F DNA sequences hybridize to two related mRNAs of 2.9 and 3.0 kilobases. When wild-type (qa-1F+) cultures are transferred to inducing conditions, qa-1F mRNA increases for 4 h, remains somewhat level, and decreases after 8 to 10 h. That this control is autogenous, i.e., that the qa-1F gene controls the synthesis of its own mRNA, is indicated by the presence of approximately the same low level of qa-1F mRNA in poly(A)+ RNA from noninducible qa-1F- mutant cultures under inducing conditions as that observed in uninduced wild-type cultures. The qa-1S gene also regulates the transcription of qa-1F, since a qa-1S- mutant, whether in noninducing or inducing conditions, contains a level of qa-1F mRNA that corresponds to the low level observed in uninduced wild-type cultures. These results corroborate the hypothesis (M. E. Case and N. H. Giles, Proc. Natl. Acad. Sci. USA 72:553-557, 1975; V. B. Patel, M. Schweizer, C. C. Dykstra, S. R. Kushner, and N. H. Giles, Proc. Natl. Acad. Sci. USA 78:5783-5787, 1981; L. Huiet, Proc. Natl. Acad. Sci. USA 81:1174-1178, 1984) that the qa-1F gene encodes an activator protein and acts positively in controlling transcription of itself and the other qa genes.

Functional domains of the yeast regulatory protein GAL4

In the yeast Saccharomyces cerevisiae regulation of the galactose/melibiose regulon rests on a dosage-dependent functional interplay between the positive regulator of transcription, the GAL4 protein, and the negative regulator, GAL80 protein. We have used this interplay to select in vitro generated fusions between the yeast ADH1 promoter and GAL4 coding sequence that overproduce GAL4 protein, allowing the identification of GAL4 protein in crude extracts from yeast. One type of these constructions produces a GAL4 protein that lacks its normal NH2 terminus. This protein is unable to complement a gal4 lesion but still retains a domain that functionally antagonizes the negative regulatory protein. One defect in this truncated protein is its inability to be concentrated in the nucleus. However, the nuclear localization defect is complemented by full-length GAL4 protein. The truncated protein also appears to effect changes in the relative transcriptional levels of the structural genes. These observations imply that GAL4 protein consists of several domains, including ones for nuclear localization, interaction with the negative regulatory protein, and, possibly, separable transcriptional activation domains for the structural genes.

Duplicate upstream activating sequences in the promoter region of the Saccharomyces cerevisiae GAL7 gene

We constructed a series of deletions in the 5' noncoding region of the Saccharomyces cerevisiae GAL7 gene, fused them to the Escherichia coli gene lacZ, and introduced them into yeasts by using a multicopy vector. We then studied the effect of the deletions on beta-galactosidase synthesis directed by the gene fusions in media with various carbon sources. This analysis identified a TATA box and two upstream activating sequences as necessary elements for galactose-controlled GAL7 transcription. Two upstream activating sequences exhibiting 71% homology with each other were located 255 and 168 base pairs, respectively, upstream of the GAL7 transcription start point. Each sequence consists of 21 base pairs, displaying an approximate rotational symmetry with a core consensus sequence of GAA--AGCTGCTTC--CGCG. At least one of the two sequences is required for galactose induction and also for glucose repression of the GAL7'-lac'Z gene. Analysis with host regulatory mutants delta gal14 and delta gal180 suggests that these sequences are the site at which the GAL4 product exerts its action to activate the GAL7 gene. We also observed that a deletion lacking both upstream activation sequences allowed the gene fusion to be expressed in the absence of galactose at about 10% of the fully induced level of the intact fusion. This constitutive expression depended on the presence of the TATA box of GAL7 in cis but not on a functional GAL4 gene. The level of the uncontrolled expression was decreased by increasing the distance between the TATA box and the pBR322 sequence in the vector plasmid.

Control of cell growth and division in Saccharomyces cerevisiae

Considerable advances have been made in recent years in our understanding of the biochemistry of protein and nucleic acid synthesis and, particularly, the molecular biology of gene expression in eukaryotes. The yeast Saccharomyces cerevisiae, and to a lesser extent Schizosaccharomyces pombe, has had a preeminent role as a focus for these studies, principally because of the facility with which these organisms can be experimentally manipulated biochemically and genetically. This review will be designed to critically examine and integrate recent advances in several vital areas of regulatory control of enzyme synthesis in yeast: structure and organization of DNA, transcriptional regulation, post-transcriptional modification, control of translation, post-translational modification and secretion, and cell-cycle modulation. It will attempt to emphasize and illustrate, where detailed information is available, principal underlying molecular mechanisms, and it will attempt to make relevant comparisons of this material to inferred and demonstrated facets of regulatory control of enzyme and protein synthesis in higher eukaryotes.

A region flanking the GAL7 gene and a binding site for GAL4 protein as upstream activating sequences in yeast

A region of DNA 116 to 271 base-pairs upstream from the GAL7 gene of Saccharomyces cerevisiae activates transcription from a heterologous promoter and does so in either orientation, showing that the GAL7 upstream region contains an upstream activating sequence (UAS). The level of transcription obtained with two GAL7 UAS's in tandem was only 1.3 times that with one. Previous studies of the GAL1-GAL10 intergenic region were indicative of two binding sites for the GAL4 positive regulatory protein; we find that a single (synthetic) site is capable of gene activation. The level of transcription obtained with the intact GAL1-GAL10 UAS was five times that with the single site.

Autogenous regulation of the positive regulatory qa-1F gene in Neurospora crassa

In Neurospora crassa, the qa-1F regulatory gene positively controls transcription of all genes in the quinic acid (qa) gene cluster. qa-1F is transcribed at a low, uninduced level but is subject to strong (50-fold), autogenous regulation as well as to control by the negative regulatory gene, qa-1S, and the inducer quinic acid. Cloned qa-1F DNA sequences hybridize to two related mRNAs of 2.9 and 3.0 kilobases. When wild-type (qa-1F+) cultures are transferred to inducing conditions, qa-1F mRNA increases for 4 h, remains somewhat level, and decreases after 8 to 10 h. That this control is autogenous, i.e., that the qa-1F gene controls the synthesis of its own mRNA, is indicated by the presence of approximately the same low level of qa-1F mRNA in poly(A)+ RNA from noninducible qa-1F- mutant cultures under inducing conditions as that observed in uninduced wild-type cultures. The qa-1S gene also regulates the transcription of qa-1F, since a qa-1S- mutant, whether in noninducing or inducing conditions, contains a level of qa-1F mRNA that corresponds to the low level observed in uninduced wild-type cultures. These results corroborate the hypothesis (M. E. Case and N. H. Giles, Proc. Natl. Acad. Sci. USA 72:553-557, 1975; V. B. Patel, M. Schweizer, C. C. Dykstra, S. R. Kushner, and N. H. Giles, Proc. Natl. Acad. Sci. USA 78:5783-5787, 1981; L. Huiet, Proc. Natl. Acad. Sci. USA 81:1174-1178, 1984) that the qa-1F gene encodes an activator protein and acts positively in controlling transcription of itself and the other qa genes.

The nucleotide sequence of the yeast MEL1 gene

The complete nucleotide sequence of the MEL1 gene of the yeast, Saccharomyces cerevisiae, encoding alpha-galactosidase was determined. The nucleotide sequence contains an open reading frame of 1413 bp encoding a protein of 471 amino acids. Comparison with the known N-terminal amino acid sequence of the mature secreted protein indicated that alpha-galactosidase is synthesized as a precursor with an N-terminal signal sequence of 18 amino acids. The general features of this signal peptide resemble those of other yeast signal peptides. Molecular weight of the mature alpha-galactosidase polypeptide deduced from the nucleotide sequence is 50.049 kd. The 5' regulatory region has sequences in common with other yeast genes regulated by the GAL4-protein.

Isolation and characterization of a phosphoprotein phosphatase-deficient mutant in yeast

The ppd1 mutant of yeast, Saccharomyces cerevisiae, was isolated as a suppressor of the cyr2 mutation which caused alteration of the catalytic subunit of cAMP-dependent protein kinase. Three peaks of phosphoprotein phosphatase activity (peak I, II and III) were identified by DEAE-Sephacel chromatography of crude extracts of the wild-type strain. The ppd1 mutant was deficient in peak III phosphoprotein phosphatase activity. The peak III enzyme efficiently utilized the phosphorylated forms of NAD-dependent glutamate dehydrogenase and trehalase as substrate. The ppd1 mutation did not suppress the cyr1, CYR3 or ras1 ras2 mutations. The ppd1 locus was located on chromosome II and had identical characteristics with glc1. The ppd1 mutation suppressed the G1 arrest caused by nutritional limitation, but maintained sensitivity to mating pheromone. In diploids homozygous for the ppd1 mutation, no premeiotic DNA replication and commitment to intragenic recombination occurred and no spores were formed, suggesting that the accumulation of phosphorylated proteins in the absence of one of the phosphoprotein phosphatases is required for mitosis but not for the initiation of meiosis.

Gene organization and regulation in the qa (quinic acid) gene cluster of Neurospora crassa

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