Isolation of the catalase T structural gene of Saccharomyces cerevisiae by functional complementation

Effects of Non-Thermal Plasma on Yeast Saccharomyces cerevisiae

Cold plasmas generated by various electrical discharges can affect cell physiology or induce cell damage that may often result in the loss of viability. Many cold plasma-based technologies have emerged in recent years that are aimed at manipulating the cells within various environments or tissues. These include inactivation of microorganisms for the purpose of sterilization, food processing, induction of seeds germination, but also the treatment of cells in the therapy. Mechanisms that underlie the plasma-cell interactions are, however, still poorly understood. Dissection of cellular pathways or structures affected by plasma using simple eukaryotic models is therefore desirable. Yeast Saccharomyces cerevisiae is a traditional model organism with unprecedented impact on our knowledge of processes in eukaryotic cells. As such, it had been also employed in studies of plasma-cell interactions. This review focuses on the effects of cold plasma on yeast cells.

Important role of catalase in the cellular response of the budding yeast Saccharomyces cerevisiae exposed to ionizing radiation

Ionizing radiation indirectly causes oxidative stress in cells via reactive oxygen species (ROS), such as hydroxyl radicals (OH(-)) generated by the radiolysis of water. We investigated how the catalase function was affected by ionizing radiation and analyzed the phenotype of mutants with a disrupted catalase gene in Saccharomyces cerevisiae exposed to radiation. The wild-type yeast strain and isogenic mutants with disrupted catalase genes were exposed to various doses of (60)Co gamma-rays. There was no difference between the wild-type strain and the cta1 disruption mutant following exposure to gamma-ray irradiation. In contrast, there was a significant decrease in the ctt1 disruption mutant, suggesting that this strain exhibited decreased survival on gamma-ray exposure compared with other strains. In all three strains, stationary phase cells were more tolerant to the exposure of gamma-rays than exponential phase cells, whereas the catalase activity in the wild-type strain and cta1 disruption mutant was higher in the stationary phase than in the exponential phase. These data suggest a correlation between catalase activity and survival following gamma-ray exposure. However, this correlation was not clear in the ctt1 disruption mutant, suggesting that other factors are involved in the tolerance to ROS induced by irradiation.

Oversynthesis of riboflavin in the yeast Pichia guilliermondii is accompanied by reduced catalase and superoxide dismutases activities

Iron deficiency causes oversynthesis of riboflavin in several yeast species, known as flavinogenic yeasts. Under iron deprivation conditions, Pichia guilliermondii cells increase production of riboflavin and malondialdehyde and the formation of protein carbonyl groups, which reflect increased intracellular content of reactive oxygen species. In this study, we found that P. guilliermondii iron deprived cells showed dramatically decreased catalase and superoxide dismutase activities. Previously reported mutations rib80, rib81, and hit1, which affect repression of riboflavin synthesis and iron accumulation by iron ions, caused similar drops in activities of the mentioned enzymes. These findings could explain the previously described development of oxidative stress in iron deprived or mutated P. guilliermondii cells that overproduce riboflavin. Similar decrease in superoxide dismutase activities was observed in iron deprived cells in the non-flavinogenic yeast Saccharomyces cerevisiae.

Differential control of Zap1-regulated genes in response to zinc deficiency in Saccharomyces cerevisiae

BACKGROUND

The Zap1 transcription factor is a central player in the response of yeast to changes in zinc status. We previously used transcriptome profiling with DNA microarrays to identify 46 potential Zap1 target genes in the yeast genome. In this new study, we used complementary methods to identify additional Zap1 target genes.

RESULTS

With alternative growth conditions for the microarray experiments and a more sensitive motif identification algorithm, we identified 31 new potential targets of Zap1 activation. Moreover, an analysis of the response of Zap1 target genes to a range of zinc concentrations and to zinc withdrawal over time demonstrated that these genes respond differently to zinc deficiency. Some genes are induced under mild zinc deficiency and act as a first line of defense against this stress. First-line defense genes serve to maintain zinc homeostasis by increasing zinc uptake, and by mobilizing and conserving intracellular zinc pools. Other genes respond only to severe zinc limitation and act as a second line of defense. These second-line defense genes allow cells to adapt to conditions of zinc deficiency and include genes involved in maintaining secretory pathway and cell wall function, and stress responses.

CONCLUSION

We have identified several new targets of Zap1-mediated regulation. Furthermore, our results indicate that through the differential regulation of its target genes, Zap1 prioritizes mechanisms of zinc homeostasis and adaptive responses to zinc deficiency.

Oxidative stress is involved in heat-induced cell death in Saccharomyces cerevisiae

The cause for death after lethal heat shock is not well understood. A shift from low to intermediate temperature causes the induction of heat-shock proteins in most organisms. However, except for HSP104, a convincing involvement of heat-shock proteins in the development of stress resistance has not been established in Saccharomyces cerevisiae. This paper shows that oxidative stress and antioxidant enzymes play a major role in heat-induced cell death in yeast. Mutants deleted for the antioxidant genes catalase, superoxide dismutase, and cytochrome c peroxidase were more sensitive to the lethal effect of heat than isogenic wild-type cells. Overexpression of catalase and superoxide dismutase genes caused an increase in thermotolerance. Anaerobic conditions caused a 500- to 20,000-fold increase in thermotolerance. The thermotolerance of cells in anaerobic conditions was immediately abolished upon oxygen exposure. HSP104 is not responsible for the increased resistance of anaerobically grown cells. The thermotolerance of anaerobically grown cells is not due to expression of heat-shock proteins. By using an oxidation-dependent fluorescent molecular probe a 2- to 3-fold increase in fluorescence was found upon heating. Thus, we conclude that oxidative stress is involved in heat-induced cell death.

Identification of essential nucleotides in an upstream repressing sequence of Saccharomyces cerevisiae by selection for increased expression of TRK2

The TRK2 gene in Saccharomyces cerevisiae encodes a membrane protein involved in potassium transport and is expressed at extremely low levels. Dominant cis-acting mutations (TRK2D), selected by their ability to confer TRK2-dependent growth on low-potassium medium, identified an upstream repressor element (URS1-TRK2) in the TRK2 promoter. The URS1-TRK2 sequence (5'-AGCCGCACG-3') shares six nucleotides with the ubiquitous URS1 element (5'-AGCCGCCGA-3'), and the protein species binding URS1-CAR1 (URSF) is capable of binding URS1-TRK2 in vitro. Sequence analysis of 17 independent repression-defective TRK2D mutations identified three adjacent nucleotides essential for URS1-mediated repression in vivo. Our results suggest a role for context effects with regard to URS1-related sequences: several mutant alleles of the URS1 element previously reported to have little or no effect when analyzed within the context of a heterologous promoter (CYC1) [Luche, R.M., Sumrada, R. & Cooper, T.G. (1990) Mol. Cell. Biol. 10, 3884-3895] have major effects on repression in the context of their native promoters (TRK2 and CAR1). TRK2D mutations that abolish repression also reveal upstream activating sequence activity either within or adjacent to URS1. Additivity between TRK2D and sin3 delta mutations suggest that SIN3-mediated repression is independent of that mediated by URS1.

NADPH binding and control of catalase compound II formation: comparison of bovine, yeast, and Escherichia coli enzymes

1. NADPH binds to bovine catalase and to yeast catalases A and T, but not to Escherichia coli catalase HPII. The association was demonstrated using chromatography and fluorimetry. Bound NADPH fluoresces in a similar way to NADPH in solution. 2. Bound NADPH protects bovine and yeast catalases against forming inactive peroxide compound II either via endogenous reductant action or by ferrocyanide reduction during catalytic activity in the presence of slowly generated peroxide. 3. Bound NADPH reduces neither compound I nor compound II of catalase. It apparently reacts with an intermediate formed during the decay of compound I to compound II; this postulated intermediate is an immediate precursor of stable compound II either when the latter is formed by endogenous reductants or when ferrocyanide is used. It represents therefore a new type of hydrogen donor that is not included in the original classification of Keilin and Nicholls [Keilin, D. and Nicholls, P. (1958) Biochim. Biophys. Acta 29, 302-307] 4. A model for NADPH action is presented in which concerted reduction of the ferryl iron and of a neighbouring protein free radical is responsible for the observed NADPH effects. The roles of migrant radical species in mammalian and yeast catalases are compared with similar events in metmyoglobin and cytochrome c peroxidase reactions with peroxides.

Regulation of Saccharomyces cerevisiae catalase gene expression by copper

Treatment of Saccharomyces cerevisiae cells with copper induces the activity of Cu/Zn superoxide dismutase (SOD) and catalase. To understand the level at which Cu regulates catalase, the expression of the S. cerevisiae CTA1 (encoding the peroxisomal catalase A) and CTT1 (encoding the cytosolic catalase T) genes was monitored as a function of Cu treatment. Copper was found to specifically induce transcription of CTT1, but not CTA1, mRNA. Moreover, genetic and biochemical studies demonstrate that this induction is independent of the ACE1 Cu trans-activator controlling the expression of yeast Cu/Zn SOD and metallothionein genes. Copper regulation of CTT1 thus appears to represent a novel metal regulatory pathway in S. cerevisiae cells.

The yeast UME6 gene product is required for transcriptional repression mediated by the CAR1 URS1 repressor binding site

URS1 is known to be a repressor binding site in Saccharomyces cerevisiae that negatively regulates expression of many genes including CAR1 (arginase), several required for sporulation, mating type switching, inositol metabolism, and oxidative carbon metabolism. In addition to the proteins previously shown to directly bind to the URS1 site, we show here that the UME6 gene product is required for URS1 to mediate repression of gene expression in the absence of inducer. We also show that mutations in the CAR80 (CARGRI) gene are allelic to those in UME6.

The Saccharomyces cerevisiae ADR1 gene is a positive regulator of transcription of genes encoding peroxisomal proteins

Expression of the CTA1 gene of Saccharomyces cerevisiae, encoding catalase A, the peroxisomal catalase of this yeast, is sensitive to glucose repression. A DNA fragment cloned as a multicopy plasmid suppressing the glucose repression of CTA1 transcription was demonstrated to contain the ADR1 gene. Multiple copies of ADR1 increased catalase A formation not only on 10% glucose, but also on ethanol medium and in the presence of oleic acid, an inducer of peroxisome proliferation. Compared with wild-type cells, adr1 null mutants produced by disruption of the gene exhibit reduced CTA1 expression. This demonstrates that ADR1 is a true positive regulator of CTA1. Further experiments showed that it acts directly on CTA1. Alcohol dehydrogenase II, which is under ADR1 control, was excluded as a mediator of the effect on CTA1; deletion of bases -123 to -168 of CTA1 reduces expression and eliminates the response to the ADR1 multicopy plasmid without eliminating fatty acid induction; and gel retardation experiments demonstrated that ADR1 binds to a CTA1 upstream fragment (-156 to -184) with limited similarity to the ADR1 binding site of ADH2. Northern hybridization experiments further demonstrated that expression of two genes encoding enzymes of peroxisomal beta-oxidation (beta-ketothiolase, trifunctional enzyme) and of a gene involved in peroxisome assembly (PAS1) is also negatively affected by the adr1 null mutation. These findings demonstrate that the ADR1 protein has much broader regulatory functions than previously recognized.

Peroxisomes in Saccharomyces cerevisiae: immunofluorescence analysis and import of catalase A into isolated peroxisomes

To isolate peroxisomes from Saccharomyces cerevisiae of a quality sufficient for in vitro import studies, we optimized the conditions for cell growth and for cell fractionation. Stability of the isolated peroxisomes was monitored by catalase latency and sedimentability of marker enzymes. It was improved by (i) using cells that were shifted to oleic acid medium after growth to stationary phase in glucose precultures, (ii) shifting the pH from 7.2 to 6.0 during cell fractionation, and (iii) carrying out equilibrium density centrifugation with Nycodenz containing 0.25 M sucrose throughout the gradient. A concentrated peroxisomal fraction was used for in vitro import of catalase A. After 2 h of incubation, 62% of the catalase was associated with, and 16% was imported into, the organelle in a protease-resistant fashion. We introduced immunofluorescence microscopy for S. cerevisiae peroxisomes, using antibodies against thiolase, which allowed us to identify even the extremely small organelles in glucose-grown cells. Peroxisomes from media containing oleic acid were larger in size, were greater in number, and had a more intense fluorescence signal. The peroxisomes were located, sometimes in clusters, in the cell periphery, often immediately adjacent to the plasma membrane. Systematic immunofluorescence observations of glucose-grown S. cerevisiae demonstrated that all such cells contained at least one and usually several very small peroxisomes despite the glucose repression. This finding fits a central prediction of our model of peroxisome biogenesis: peroxisomes form by division of preexisting peroxisomes; therefore, every cell must have at least one peroxisome if additional organelles are to be induced in that cell.

The Saccharomyces cerevisiae ADR1 gene is a positive regulator of transcription of genes encoding peroxisomal proteins

Expression of the CTA1 gene of Saccharomyces cerevisiae, encoding catalase A, the peroxisomal catalase of this yeast, is sensitive to glucose repression. A DNA fragment cloned as a multicopy plasmid suppressing the glucose repression of CTA1 transcription was demonstrated to contain the ADR1 gene. Multiple copies of ADR1 increased catalase A formation not only on 10% glucose, but also on ethanol medium and in the presence of oleic acid, an inducer of peroxisome proliferation. Compared with wild-type cells, adr1 null mutants produced by disruption of the gene exhibit reduced CTA1 expression. This demonstrates that ADR1 is a true positive regulator of CTA1. Further experiments showed that it acts directly on CTA1. Alcohol dehydrogenase II, which is under ADR1 control, was excluded as a mediator of the effect on CTA1; deletion of bases -123 to -168 of CTA1 reduces expression and eliminates the response to the ADR1 multicopy plasmid without eliminating fatty acid induction; and gel retardation experiments demonstrated that ADR1 binds to a CTA1 upstream fragment (-156 to -184) with limited similarity to the ADR1 binding site of ADH2. Northern hybridization experiments further demonstrated that expression of two genes encoding enzymes of peroxisomal beta-oxidation (beta-ketothiolase, trifunctional enzyme) and of a gene involved in peroxisome assembly (PAS1) is also negatively affected by the adr1 null mutation. These findings demonstrate that the ADR1 protein has much broader regulatory functions than previously recognized.

Peroxisomes in Saccharomyces cerevisiae: immunofluorescence analysis and import of catalase A into isolated peroxisomes

To isolate peroxisomes from Saccharomyces cerevisiae of a quality sufficient for in vitro import studies, we optimized the conditions for cell growth and for cell fractionation. Stability of the isolated peroxisomes was monitored by catalase latency and sedimentability of marker enzymes. It was improved by (i) using cells that were shifted to oleic acid medium after growth to stationary phase in glucose precultures, (ii) shifting the pH from 7.2 to 6.0 during cell fractionation, and (iii) carrying out equilibrium density centrifugation with Nycodenz containing 0.25 M sucrose throughout the gradient. A concentrated peroxisomal fraction was used for in vitro import of catalase A. After 2 h of incubation, 62% of the catalase was associated with, and 16% was imported into, the organelle in a protease-resistant fashion. We introduced immunofluorescence microscopy for S. cerevisiae peroxisomes, using antibodies against thiolase, which allowed us to identify even the extremely small organelles in glucose-grown cells. Peroxisomes from media containing oleic acid were larger in size, were greater in number, and had a more intense fluorescence signal. The peroxisomes were located, sometimes in clusters, in the cell periphery, often immediately adjacent to the plasma membrane. Systematic immunofluorescence observations of glucose-grown S. cerevisiae demonstrated that all such cells contained at least one and usually several very small peroxisomes despite the glucose repression. This finding fits a central prediction of our model of peroxisome biogenesis: peroxisomes form by division of preexisting peroxisomes; therefore, every cell must have at least one peroxisome if additional organelles are to be induced in that cell.

A cis-acting element present in multiple genes serves as a repressor protein binding site for the yeast CAR1 gene

Induction of the arginase (CAR1) gene expression in Saccharomyces cerevisiae has previously been shown to require participation of a cis-dominantly regulated upstream repression sequence (URS). Deletion of this element results in high-level expression of the CAR1 gene without inducer. To determine the structure of the CAR1 URS element, we performed a saturation mutagenesis. Results of the mutagenic analysis indicated that the CAR1 URS was a 9-base-pair palindromic sequence, 5'-AGCCGCCGA-3'. A DNA fragment containing this sequence was shown to bind one or more proteins by a gel shift assay. DNA fragments containing point mutations that completely eliminated URS function were not effective competitors in this assay, whereas those which supported URS function were effective competitors. Sequences in the 5'-flanking regions of 14 other genes were found to be homologous to the CAR1 URS. These sequences were shown to support varying degrees of URS function in the expression vector assay, to bind protein as demonstrated by the gel shift assay, and to compete with a DNA fragment containing the CAR1 URS for protein binding. These results indicate that the CAR1 URS element possesses the characteristics of a repressor binding site. Further, they are consistent with the suggestion that sites homologous to the CAR1 URS may be situated in the 5'-flanking regions of multiple unrelated yeast genes. The widespread occurrence of this element raises the possibility that it is the target site for one or more negatively acting general transcription factors.

A cis-acting element present in multiple genes serves as a repressor protein binding site for the yeast CAR1 gene

Induction of the arginase (CAR1) gene expression in Saccharomyces cerevisiae has previously been shown to require participation of a cis-dominantly regulated upstream repression sequence (URS). Deletion of this element results in high-level expression of the CAR1 gene without inducer. To determine the structure of the CAR1 URS element, we performed a saturation mutagenesis. Results of the mutagenic analysis indicated that the CAR1 URS was a 9-base-pair palindromic sequence, 5'-AGCCGCCGA-3'. A DNA fragment containing this sequence was shown to bind one or more proteins by a gel shift assay. DNA fragments containing point mutations that completely eliminated URS function were not effective competitors in this assay, whereas those which supported URS function were effective competitors. Sequences in the 5'-flanking regions of 14 other genes were found to be homologous to the CAR1 URS. These sequences were shown to support varying degrees of URS function in the expression vector assay, to bind protein as demonstrated by the gel shift assay, and to compete with a DNA fragment containing the CAR1 URS for protein binding. These results indicate that the CAR1 URS element possesses the characteristics of a repressor binding site. Further, they are consistent with the suggestion that sites homologous to the CAR1 URS may be situated in the 5'-flanking regions of multiple unrelated yeast genes. The widespread occurrence of this element raises the possibility that it is the target site for one or more negatively acting general transcription factors.

Control of Saccharomyces cerevisiae catalase T gene (CTT1) expression by nutrient supply via the RAS-cyclic AMP pathway

In Saccharomyces cerevisiae, lack of nutrients triggers a pleiotropic response characterized by accumulation of storage carbohydrates, early G1 arrest, and sporulation of a/alpha diploids. This response is thought to be mediated by RAS proteins, adenylate cyclase, and cyclic AMP (cAMP)-dependent protein kinases. This study shows that expression of the S. cerevisiae gene coding for a cytoplasmic catalase T (CTT1) is controlled by this pathway: it is regulated by the availability of nutrients. Lack of a nitrogen, sulfur, or phosphorus source causes a high-level expression of the gene. Studies with strains with mutations in the RAS-cAMP pathway and supplementation of a rca1 mutant with cAMP show that CTT1 expression is under negative control by a cAMP-dependent protein kinase and that nutrient control of CTT1 gene expression is mediated by this pathway. Strains containing a CTT1-Escherichia coli lacZ fusion gene have been used to isolate mutants with mutations in the pathway. Mutants characterized in this investigation fall into five complementation groups. Both cdc25 and ras2 alleles were identified among these mutants.

Control of the Saccharomyces cerevisiae regulatory gene PET494: transcriptional repression by glucose and translational induction by oxygen

The product of the Saccharomyces cerevisiae nuclear gene PET494 is required to promote the translation of the mitochondrial mRNA encoding cytochrome c oxidase subunit III (coxIII). The level of cytochrome c oxidase activity is affected by several different environmental conditions, which also influence coxIII expression. We have studied the regulation of PET494 to test whether the level of its expression might modulate coxIII translation in response to these conditions. A pet494::lacZ fusion was constructed and used to monitor PET494 expression. PET494 was regulated by oxygen availability: expression in a respiration-competent diploid strain grown anaerobically was one-fifth the level of expression in aerobically grown cells. However, since PET494 mRNA levels did not vary in response to oxygen deprivation, regulation by oxygen appears to occur at the translational level. This oxygen regulation was not mediated by heme, and PET494 expression was independent of the heme activator protein HAP2. The regulation of PET494 expression by carbon source was also examined. In cells grown on glucose-containing medium, PET494 was expressed at levels four- to sixfold lower than in cells grown on ethanol and glycerol. However, addition of ethanol to glucose-containing medium induced PET494 expression approximately twofold. PET494 transcript levels varied over a fourfold range in response to different carbon sources. The effects on PET494 expression of mutations in the SNF1, SNF2, SSN6, and HXK2 genes were also determined and found to be minimal.

Control of Saccharomyces cerevisiae catalase T gene (CTT1) expression by nutrient supply via the RAS-cyclic AMP pathway

In Saccharomyces cerevisiae, lack of nutrients triggers a pleiotropic response characterized by accumulation of storage carbohydrates, early G1 arrest, and sporulation of a/alpha diploids. This response is thought to be mediated by RAS proteins, adenylate cyclase, and cyclic AMP (cAMP)-dependent protein kinases. This study shows that expression of the S. cerevisiae gene coding for a cytoplasmic catalase T (CTT1) is controlled by this pathway: it is regulated by the availability of nutrients. Lack of a nitrogen, sulfur, or phosphorus source causes a high-level expression of the gene. Studies with strains with mutations in the RAS-cAMP pathway and supplementation of a rca1 mutant with cAMP show that CTT1 expression is under negative control by a cAMP-dependent protein kinase and that nutrient control of CTT1 gene expression is mediated by this pathway. Strains containing a CTT1-Escherichia coli lacZ fusion gene have been used to isolate mutants with mutations in the pathway. Mutants characterized in this investigation fall into five complementation groups. Both cdc25 and ras2 alleles were identified among these mutants.

Control of the Saccharomyces cerevisiae regulatory gene PET494: transcriptional repression by glucose and translational induction by oxygen

The product of the Saccharomyces cerevisiae nuclear gene PET494 is required to promote the translation of the mitochondrial mRNA encoding cytochrome c oxidase subunit III (coxIII). The level of cytochrome c oxidase activity is affected by several different environmental conditions, which also influence coxIII expression. We have studied the regulation of PET494 to test whether the level of its expression might modulate coxIII translation in response to these conditions. A pet494::lacZ fusion was constructed and used to monitor PET494 expression. PET494 was regulated by oxygen availability: expression in a respiration-competent diploid strain grown anaerobically was one-fifth the level of expression in aerobically grown cells. However, since PET494 mRNA levels did not vary in response to oxygen deprivation, regulation by oxygen appears to occur at the translational level. This oxygen regulation was not mediated by heme, and PET494 expression was independent of the heme activator protein HAP2. The regulation of PET494 expression by carbon source was also examined. In cells grown on glucose-containing medium, PET494 was expressed at levels four- to sixfold lower than in cells grown on ethanol and glycerol. However, addition of ethanol to glucose-containing medium induced PET494 expression approximately twofold. PET494 transcript levels varied over a fourfold range in response to different carbon sources. The effects on PET494 expression of mutations in the SNF1, SNF2, SSN6, and HXK2 genes were also determined and found to be minimal.

Ubiquitous upstream repression sequences control activation of the inducible arginase gene in yeast

Expression of the yeast arginase gene (CAR1) responds to both induction and nitrogen catabolite repression. Regulation is mediated through sequences that both positively and negatively modulate CAR1 transcription. A short sequence, 5'-TAGCCGCCGAGGG-3', possessing characteristics of a repressor binding site, plays a central role in the induction process. A fragment containing this upstream repression sequence (URS1) repressed gene expression when placed either 5' or 3' to the upstream activation sequences of the heterologous gene CYC1. Action of the URS and its cognate repressor was overcome by CAR1 induction when the URS was situated cis to the CAR1 flanking sequences. This was not observed, however, when it was situated downstream of a heterologous CYC1 upstream activation sequence indicating that URS function is specifically neutralized by cis-acting elements associated with CAR1 induction. Searches of sequences in various gene banks revealed that URS1-like sequences occur ubiquitously in genetic regulatory regions including those of bacteriophage lambda, yeast, mammalian, and viral genes. In a significant number of cases the sequence is contained in a region associated with negative control of yeast gene regulation. These data suggest the URS identified in this work is a generic repressor target site that apparently has been conserved during the evolution of transcriptional regulatory systems.

Heme control region of the catalase T gene of the yeast Saccharomyces cerevisiae

The 5'-flanking region of the Saccharomyces cerevisiae catalase T gene (CTT1) and the part of the gene coding for the N-terminus of catalase T were sequenced. 5'-Ends of transcripts of the region were located by S1 nuclease mapping and primer extension. To analyse control elements in the upstream region, a CTT1-lacZ gene fusion was constructed. Deletion analysis was carried out within a part of the 5'-flanking region showing homology to the upstream region of the yeast CYC1 gene. Like the CTT1 gene, this gene is controlled by heme, oxygen and glucose. The results obtained show that the CTT1 gene is positively controlled by heme. Tentative evidence has been obtained for the involvement of upstream sequences homologous to UAS1 and UAS2 of the CYC1 gene in heme control. Further, a negative site has been located between the upstream activator sites and the transcription start. Within this negative region a ten base-pair sequence was detected that shows high homology to a sequence located within a negative control region of the CYC1 gene and some homology to the negative control elements of the S. cerevisiae CAR1 and CAR2 genes.

Isolation of the catalase A gene of Saccharomyces cerevisiae by complementation of the cta1 mutation

As a first step in an analysis of the DNA regions involved in the control of the catalase A gene of Saccharomyces cerevisiae by glucose, heme, and oxygen this gene has been cloned. Catalase A-deficient mutants were obtained by UV mutagenesis of a ctt1 mutant strain specifically lacking catalase T. All the catalase A-deficient mutants obtained fall into one complementation group. The single recessive mutation causing specific lack of catalase A was designated cta1. Several overlapping DNA fragments complementing the cta1 mutation were obtained by transforming ctt1 cta1 double mutants with a yeast gene library in vector YEp13. Hybrid selection of RNA with the help of one of the cloned DNAs followed by in vitro translation of this RNA and identification of the protein synthesized with catalase A-specific antibodies showed that the catalase A structural gene has been cloned. A single copy of this gene is present in the yeast genome. Transcription of the catalase A gene cloned into vector YEp13 is repressed by glucose. The DNA isolated hybridizes to a 1.6 kb polyA+-RNA virtually absent from heme-deficient cells, presumably catalase A mRNA.

Genetic mapping of katF, a locus that with katE affects the synthesis of a second catalase species in Escherichia coli

A class of catalase-deficient mutants that was unlinked to katE was localized between mutS and cys at 59.0 min on the Escherichia coli genome. This locus was named katF. Transposon Tn10 insertions were isolated that mapped in both katE and katF loci. The catalase species present in katE+ and katF+ recombinants was found to be different from the main catalase activities, HPI and HPII, in several respects. It did not have an associated peroxidase activity; it was electrophoretically slower on native polyacrylamide gels; it eluted from DEAE-Sephadex A50 at a higher salt concentration; its Km for H2O2 was 30.9 mM as compared with 3.7 mM for HPI and HPII; its synthesis was not induced by ascorbate; and it did not cross react with HPI-HPII antisera. This new catalase was labeled HPIII.