Dps Gene Research Articles

Synergistic effects of chromosomal ispB deletion and dxs overexpression on coenzyme Q 10 production in recombinant Escherichia coli expressing Agrobacterium tumefaciens dps gene

For biotechnological production of coenzyme Q 10 (CoQ 10) in recombinant Escherichia coli, three genetic manipulations were performed: heterologous expression of decaprenyl diphosphate synthase (Dps) from Agrobacterium tumefaciens, deletion of endogenous octaprenyl diphosphate synthase (IspB), and overexpression of 1-deoxy- d-xylulose synthase (Dxs). Expression of the dps gene and deletion of the ispB gene in E. coli BL21(DE3)Δ ispB/pAP1 allowed production of CoQ 10 only. Furthermore, coexpression of the dxs gene increased the specific content of CoQ 10 from 0.55–0.89 mg g −1 to 1.40 mg g −1. For mass production of CoQ 10, fed-batch fermentation of E. coli BL21(DE3)Δ ispB/pAP1 + pDXS was carried out in a defined medium with 20 g l −1 initial glucose and by the glucose-feeding strategy of pH-stat. Finally, 99.4 mg l −1 CoQ 10 concentration, 1.41 mg g −1 specific CoQ 10 content and 3.11 mg l −1 h −1 productivity were obtained in 33 h of the fermentation, which were 78, 1.9, and 19 times higher than those for E. coli BL21(DE3)/pAP1 without the ispB deletion and dxs overexpression.

Characterization of an acquireddps-containing gene island in the lactic acid bacteriumOenococcus oeni

To identify novel actors responsible for the marked adaptation of the Oenococcus oeni species to its environment. Genomic surveillance of the available genome sequences from O. oeni indicated the presence of a small ORF, encoding a protein named Dps(A). The cloned gene complemented the dps(-) mutant of Escherichia coli and conferred resistance to hydrogen peroxide, wine, and metals. The dps(A) gene was flanked by IS-related elements. The entire region was characterized by an anomalously high GC content compared to those reported for oenococcal genomes. The dps(A) gene was present in 15 of the 38 tested isolates. Positive strains originated from different geographical areas and sources. No change in tolerance to wine or to oxidative stress was observed between O. oeni strains harbouring dps(A) and those not harbouring this gene. Some O. oeni have acquired a functional homologue to the dps gene from E. coli as part of a mobile element. Dps(A) probably increases the bacterial fitness in response to environmental challenges. However, the physiological condition under which it adds a selective advantage to O. oeni during winemaking remains to be found.

Microfluidics in biology and genosensor construction

We describe key stages in the development of a genosensor-based bioanalytical complex capable of functioning in a micro/nanofluidic system (MNFS), which is intended for detecting damaging agents in liquid media. Using the LIGA technology, we have developed an MNFS with a channel width of a few microns or more. Methods of (i) processing microfluid channels for positioning bacterial cells-genosensors and (ii) detecting fluorescent signals in a microfluid module are developed. A search for promoters ensuring the response of genosensor structures to a broad range of damaging factors of the external environment is carried out using a bioinformatics approach (based on GenSensor database). An experimental genosensor has been constructed based on the dps gene promoter of E. coli and the pRS-GFPvaa vector plasmid. It is shown that an E. coli/pDps-gfp genosensor in a microfluid module responds by GFPvaa protein synthesis to the presence of oxidative stress agents and agents capable of penetrating membranes in the same range of concentrations as those outside the module. The results of our investigation show that the proposed interdisciplinary approach can be used for obtaining bacterial cells-genosensors capable of functioning in MNFSs and detecting damaging factors of the external environment.

Cloning and Functional Expression of the dps Gene Encoding Decaprenyl Diphosphate Synthase from Agrobacterium tumefaciens

A newly isolated gene from Agrobacterium tumefaciens (A. tumefaciens), which encoded a decaprenyl diphosphate synthase, was cloned in Escherichia coli (E. coli), and its nucleotide sequence was determined. DNA sequence analysis revealed an open reading frame of 1077 bp capable of encoding a 358-amino-acid protein with a calculated isoelectric point of pH 5.16 and a molecular mass of 38 960 Da. The primary structure of the enzyme shared significant homology with prenyl diphosphate synthases from various sources. The deduced amino acid sequence included oligopeptide DDxxD aspartate-rich domains conserved in the majority of prenyl diphosphate synthases. High levels of the active enzyme were expressed in the soluble fraction and were readily purified to homogeneity by Ni-NTA chromatography. E. coli JM109 harboring the dps gene produced ubiquinone-10 in addition to endogenous ubiquinone-8, while E. coli JM109 harboring the dps gene mutated on the DDxxD domain lost the ability to produce ubiquinone-10, which suggests that the A. tumefaciens dps gene is functionally expressed in E. coli and that it encodes a decaprenyl diphosphate synthase.

Selective repression by Fis and H‐NS at the Escherichia coli dps promoter

Dps is a nucleoid-associated protein that plays a major role in condensation of the Escherichia coli chromosome in stationary phase. Here we show that two other nucleoid-associated proteins, Fis and H-NS, can bind at the dps gene promoter and downregulate its activity. Both Fis and H-NS selectively repress the dps promoter, preventing transcription initiation by RNA polymerase containing sigma(70), the housekeeping sigma factor, but not by RNA polymerase containing sigma(38), the stationary-phase sigma factor. Fis represses by trapping RNA polymerase containing sigma(70) at the promoter. In contrast, H-NS functions by displacing RNA polymerase containing sigma(70), but not RNA polymerase containing sigma(38). Dps levels are known to be very low in exponentially growing cells and rise sharply as cells enter stationary phase. Conversely, Fis levels are high in growing cells but fall to nearly zero in stationary-phase cells. Our data suggest a simple model to explain how the Dps-dependent super-compaction of the folded chromosome is triggered as cell growth ceases.

Cloning, expression and purification of a glycosylated form of the DNA-binding protein Dps from Salmonella enterica Typhimurium

Dps, found in many eubacterial and archaebacterial species, appears to protect cells from oxidative stress and/or nutrient-limited environment. Dps has been shown to accumulate during the stationary phase, to bind to DNA non-specifically, and to form a crystalline structure that compacts and protects the chromosome. Our previous results have indicated that Dps is glycosylated at least for a certain period of the bacterial cell physiology and this glycosylation is thought to be orchestrated by some factors not yet understood, explaining our difficulties in standardizing the Dps purification process. In the present work, the open reading frame of the dps gene, together with all the upstream regulatory elements, were cloned into a PCR cloning vector. As a result, the expression of dps was also controlled by the plasmid system introduced in the bacterial cell. The gene was then over-expressed regardless of the growth phase of the culture and a glycosylated fraction was purified to homogeneity by lectin-immobilized chromatography assay. Unlike the high level expression of Dps in Salmonella cells, less than 1% of the recombinant protein was purified by affinity chromatography using jacalin column. Sequencing and mass spectrometry data confirmed the identity of the dps gene and the protein, respectively. In spite of the low level of purification of the jacalin-binding Dps, this work shall aid further investigations into the mechanism of Dps glycosylation.

Periplasmic Cu,Zn superoxide dismutase and cytoplasmic Dps concur in protecting Salmonella enterica serovar Typhimurium from extracellular reactive oxygen species

Several bacteria possess periplasmic Cu,Zn superoxide dismutases which can confer protection from extracellular reactive oxygen species. Thus, deletion of the sodC1 gene reduces Salmonella enterica serovar Typhimurium ability to colonize the spleens of wild type mice, but enhances virulence in p47phox mutant mice. To look into the role of periplamic Cu,Zn superoxide dismutase and into possible additive effects of the ferritin-like Dps protein involved in hydrogen peroxide detoxification, we have analyzed bacterial survival in response to extracellular sources of superoxide and/or hydrogen peroxide. Exposure to extracellular superoxide of Salmonella Typhimurium mutant strains lacking the sodC1 and sodC2 genes and/or the dps gene does not cause direct killing of bacteria, indicating that extracellular superoxide is poorly bactericidal. In contrast, all mutant strains display a sharp hydrogen peroxide-dependent loss of viability, the dps,sodC1,sodC2 mutant being less resistant than the dps or the sodC1,sodC2 mutants. These findings suggest that the role of Cu,Zn superoxide dismutase in bacteria is to remove rapidly superoxide from the periplasm to prevent its reaction with other reactive molecules. Moreover, the nearly additive effect of the sodC and dps mutations suggests that localization of antioxidant enzymes in different cellular compartments is required for bacterial resistance to extracytoplasmic oxidative attack.

Expression of various genes to enhance ubiquinone metabolic pathway in Agrobacterium tumefaciens

Ubiquinone (UQ), a lipid-soluble component, acts as a mobile component of the respiratory chain by playing an essential role in the electron transport system in many organisms, and has been widely used in pharmaceuticals due to its antioxidant property. The biosynthesis of UQ involves 10 sequential reactions brought about by various enzymes. In this study, dps gene, which encodes decaprenyl diphosphate synthase, involved in ubiquinone biosynthesis from Agrobacterium tumefaciens, and coq2 gene of Saccharomyces cerevisiae, ppt1 gene of Schizosaccahromyces pombe and ubiA gene of Escherichia coli, all of them encoding 4-hydroxybenzoate:polyprenyl diphosphate (4-HB:PPP) transferase, were reconfigured into an operon under the control of a single promoter to yield various plasmids including pBIV-dps, pBIV-dpsq, pBIV-dpsp and pBIV-dpsca. The recombinant A. tumefaciens containing dps-ubiC-ubiA gene showed the highest level ubiquinone production than that of the other recombinants and the nonrecombinant bacterium. In an aerobic fed-batch fermentation, A. tumefaciens containing the pBIV-dpsca plasmid produced 25.2 mg of ubiquinone-10 per liter which was 1.68 times higher than that of nonrecombinant type. While in microaerobic fed-batch fermentation, recombinant cell pBIV-dpsca produced 30.8 mg L −1 of ubiquinone-10. Compared to the original A. tumefaciens, the ubiquinone-10 yield and productivities of the recombinant bacterium pBIV-dpsca increased 88.9% and 77.7%, respectively, under microaerobic fed-batch conditions.

The ArcA regulon and oxidative stress resistance in Haemophilus influenzae.

Haemophilus influenzae transits between niches within the human host that are predicted to differ in oxygen levels. The ArcAB two-component signal transduction system controls gene expression in response to respiratory conditions of growth and has been implicated in bacterial pathogenesis, yet the mechanism is not understood. We undertook a genome-scale study to identify genes of the H. influenzae ArcA regulon. Deletion of arcA resulted in increased anaerobic expression of genes of the respiratory chain and of H. influenzae's partial tricarboxylic acid cycle, and decreased anaerobic expression levels of genes of polyamine metabolism, and iron sequestration. Deletion of arcA also conferred a susceptibility to transient exposure to hydrogen peroxide that was greater following anaerobic growth than after aerobic growth. Array data revealed that the dps gene, not previously assigned to the ArcA modulon in bacteria, exhibited decreased expression in the arcA mutant. Deletion of dps resulted in hydrogen peroxide sensitivity and complementation restored resistance, providing insight into the previously uncharacterized mechanism of arcA-mediated H2O2 resistance. The results indicate a role for H. influenzae arcA and dps in pre-emptive defence against transitions from growth in low oxygen environments to aerobic exposure to hydrogen peroxide, an antibacterial oxidant produced by phagocytes during infection.

APPLICATION OF BIOINFORMATICS RESOURCES FOR GENOSENSOR DESIGN

Two novel databases, GenSensor and ConSensor, have been developed. GenSensor accumulates information on the sensitivities of the prokaryotic genes to external stimuli and may facilitate designing of novel genosensors; ConSensor contains data about the structure and efficiency of the available genosensor plasmid constructs. Using these databases, candidate genes for the design of novel multiple functional genosensors were searched, and the Escherichia coli dps gene was chosen as the candidate. The genetic construct derived from its promoter was developed and tested for its sensitivity to various stress agents: hydrogen peroxide (oxidative stress), phenol (protein and membrane damaging), and mitomycin C (DNA damaging). This genosensor was found to be sensitive to all stress conditions applied confirming its ability to serve as multi-functional genosensor. The GenSensor and ConSensor databases are available at http://wwwmgs.bionet.nsc.ru/mgs/dbases/gensensor/index.html.

Ubiquinone-10 Production Using Agrobacterium tumefaciens dps Gene in Escherichia coli by Coexpression System

Ubiquinone (Coenzyme Q; abbreviation, UQ) acts as a mobile component of the respiratory chain by playing an essential role in the electron transport system, and has been widely used in pharmaceuticals. The biosynthesis of UQ involves 10 sequential reactions brought about by various enzymes. In this study we have cloned, expressed the decaprenyl diphosphate synthase, designated dps gene, from Agrobacterium tumefaciens, and succeeded in detecting UQ-10 in addition to innate UQ-8 in Escherichia coli. Furthermore, the production of UQ-10 was higher than UQ-8. To establish an efficient expression system for UQ- 10 production, we used genes, including ubiC, ubiA, and ubiG involved in UQ biosynthesis in E. coli, to construct a better co-expression system. The expression coupled by dps and ubiCA was effective for increasing UQ-10 production by five times than that by expressing single dps gene in the shake flask culture. To study for a large-scale production of UQ-10 in E. coli, fed-batch fermentations were implemented to achieve a high cell density culture. A cell concentration of 85.40 g/L and 94.58 g/L dry cell weight (DCW), and UQ-10 content of 50.29 mg/L and 45.86 mg/L was obtained after 32.5 h and 27.5 h of cultivation, subsequent to isopropyl-beta-D-thiogalactopyranoside and lactose induction, respectively. In addition, plasmid stability was maintained at high level throughout the fermentation.

Paired Bacillus anthracis Dps (Mini-ferritin) Have Different Reactivities with Peroxide

Dps (DNA protection during starvation) proteins, mini-ferritins in the ferritin superfamily, catalyze Fe(2+)/H(2)O(2)/O(2) reactions and make minerals inside protein nanocages to minimize radical oxygen-chemistry (metal/osmotic/temperature/nutrient/oxidant) and sometimes to confer virulence. Paired Dps proteins in Bacillus, rare in other bacteria, have 60% sequence identity. To explore functional differences in paired Bacilli Dps protein, we measured ferroxidase activity and DNA protection (hydroxyl radical) for Dps protein dodecamers from Bacillus anthracis (Ba) since crystal structures and iron mineralization (iron-stain) were known. The self-assembled (200 kDa) Ba Dps1 (Dlp-1) and Ba Dps2 (Dlp-2) proteins had similar Fe(2+)/O(2) kinetics, with space for minerals of 500 iron atoms/protein, and protected DNA. The reactions with Fe(2+) were novel in several ways: 1) Ba Dps2 reactions (Fe(2+)/H(2)O(2)) proceeded via an A(650 nm) intermediate, with similar rates to maxi-ferritins (Fe(2+)/O(2)), indicating a new Dps protein reaction pathway, 2) Ba Dps2 reactions (Fe(2+)/O(2) versus Fe(2+)/O(2) + H(2)O(2)) differed 3-fold contrasting with Escherichia coli Dps reactions, with 100-fold differences, and 3) Ba Dps1, inert in Fe(2+)/H(2)O(2) catalysis, inhibited protein-independent Fe(2+)/H(2)O(2) reactions. Sequence similarities between Ba Dps1 and Bacillus subtilis DpsA (Dps1), which is regulated by general stress factor (SigmaB) and Fur, and between Ba Dps2 and B. subtilis MrgA, which is regulated by H(2)O(2) (PerR), suggest the function of Ba Dps1 is iron sequestration and the function of Ba Dps2 is H(2)O(2) destruction, important in host/pathogen interactions. Destruction of H(2)O(2) by Ba Dps2 proceeds via an unknown mechanism with an intermediate similar spectrally (A(650 nm)) and kinetically to the maxi-ferritin diferric peroxo complex.

Phylogeny of bovine non-O157-Shigatoxin-producing E. coli (STEC) strains, with respect to the acquisition of the Locus of Enterocyte Effacement (LEE)

Understanding the survival mechanisms used by Shiga toxin-producing Escherichia coli (STEC), including O157:H7 and non-O157 serotypes, is important for minimizing contamination of fresh produce and occurrence of foodborne outbreaks. Recent outbreaks linked to leafy green vegetables and sprouted seeds have prompted researchers to focus on investigating decontamination strategies. Several studies showed that hydrogen peroxide (H2O2) treatment has been effective in reducing pathogens on fresh produce. As such, the effect of hydrogen peroxide on stress-associated and virulence gene expression in six STEC isolates was investigated in this study. Logarithmic phase cells of E. coli O157:H7 (EDL933) and non-O157 serotypes, including E. coli O26:H11 (EC20070549), O103:H2 (EC19970811), O104:H4 (NML#11-3088), O111:NM (EC20070546) and O145:NM (EC19970355) were exposed to 2.5 mM H2O2 for 40 min and gene expression was evaluated using quantitative real-time PCR. Different patterns of gene expression were observed in E. coli O157:H7 and non-O157 serotypes. Particularly, Shiga toxin gene stx2 was upregulated in O157:H7, but not in O104:H4. Moreover, stx1 was significantly upregulated in STEC O157:H7, but only slightly upregulated Stx1-positive non-O157 serotypes. However genes related to motility (fliC) and intimin gene (eae) were downregulated in most strains. Stress-associated sodA gene encoding manganese superoxide dismutase was significantly upregulated in all serotypes. The dps gene coding for non-specific DNA binding protein was upregulated in O145:NM, O111:NM, O103:H2 and O26:H11. However genes related to cold shock (cspC) and acid resistance (gadW) were significantly downregulated in all strains tested. The results of this study provide a basic understanding of the oxidative stress impact on survival and virulence of non-O157 serotype STEC strains.

EHP005 Discrepancies between phenotypic and molecular detection of Shiga toxin-producing Escherichia coli

Understanding the survival mechanisms used by Shiga toxin-producing Escherichia coli (STEC), including O157:H7 and non-O157 serotypes, is important for minimizing contamination of fresh produce and occurrence of foodborne outbreaks. Recent outbreaks linked to leafy green vegetables and sprouted seeds have prompted researchers to focus on investigating decontamination strategies. Several studies showed that hydrogen peroxide (H2O2) treatment has been effective in reducing pathogens on fresh produce. As such, the effect of hydrogen peroxide on stress-associated and virulence gene expression in six STEC isolates was investigated in this study. Logarithmic phase cells of E. coli O157:H7 (EDL933) and non-O157 serotypes, including E. coli O26:H11 (EC20070549), O103:H2 (EC19970811), O104:H4 (NML#11-3088), O111:NM (EC20070546) and O145:NM (EC19970355) were exposed to 2.5 mM H2O2 for 40 min and gene expression was evaluated using quantitative real-time PCR. Different patterns of gene expression were observed in E. coli O157:H7 and non-O157 serotypes. Particularly, Shiga toxin gene stx2 was upregulated in O157:H7, but not in O104:H4. Moreover, stx1 was significantly upregulated in STEC O157:H7, but only slightly upregulated Stx1-positive non-O157 serotypes. However genes related to motility (fliC) and intimin gene (eae) were downregulated in most strains. Stress-associated sodA gene encoding manganese superoxide dismutase was significantly upregulated in all serotypes. The dps gene coding for non-specific DNA binding protein was upregulated in O145:NM, O111:NM, O103:H2 and O26:H11. However genes related to cold shock (cspC) and acid resistance (gadW) were significantly downregulated in all strains tested. The results of this study provide a basic understanding of the oxidative stress impact on survival and virulence of non-O157 serotype STEC strains.

The Dps Protein of Agrobacterium tumefaciens Does Not Bind to DNA but Protects It toward Oxidative Cleavage: X-RAY CRYSTAL STRUCTURE, IRON BINDING, AND HYDROXYL-RADICAL SCAVENGING PROPERTIES

Agrobacterium tumefaciens Dps (DNA-binding proteins from starved cells), encoded by the dps gene located on the circular chromosome of this plant pathogen, was cloned, and its structural and functional properties were determined in vitro. In Escherichia coli Dps, the family prototype, the DNA binding properties are thought to be associated with the presence of the lysine-containing N-terminal tail that extends from the protein surface into the solvent. The x-ray crystal structure of A. tumefaciens Dps shows that the positively charged N-terminal tail, which is 11 amino acids shorter than in the E. coli protein, is blocked onto the protein surface. This feature accounts for the lack of interaction with DNA. The intersubunit ferroxidase center characteristic of Dps proteins is conserved and confers to the A. tumefaciens protein a ferritin-like activity that manifests itself in the capacity to oxidize and incorporate iron in the internal cavity and to release it after reduction. In turn, sequestration of Fe(II) correlates with the capacity of A. tumefaciens Dps to reduce the production of hydroxyl radicals from H2O2 through Fenton chemistry. These data demonstrate conclusively that DNA protection from oxidative damage in vitro does not require formation of a Dps-DNA complex. In vivo, the hydroxyl radical scavenging activity of A. tumefaciens Dps may be envisaged to act in concert with catalase A to counteract the toxic effect of H2O2, the major component of the plant defense system when challenged by the bacterium.

Contribution of dps to acid stress tolerance and oxidative stress tolerance in Escherichia coli O157:H7.

An Escherichia coli O157:H7 dps::nptI mutant (FRIK 47991) was generated, and its survival was compared to that of the parent in HCl (synthetic gastric fluid, pH 1.8) and hydrogen peroxide (15 mM) challenges. The survival of the mutant in log phase (5-h culture) was significantly impaired (4-log(10)-CFU/ml reduction) compared to that of the parent strain (ca. 1.0-log(10)-CFU/ml reduction) after a standard 3-h acid challenge. Early-stationary-phase cells (12-h culture) of the mutant decreased by ca. 4 log(10) CFU/ml while the parent strain decreased by approximately 2 log(10) CFU/ml. No significant differences in the survival of late-stationary-phase cells (24-h culture) between the parent strain and the mutant were observed, although numbers of the parent strain declined less in the initial 1 h of acid challenge. FRIK 47991 was more sensitive to hydrogen peroxide challenge than was the parent strain, although survival improved in stationary phase. Complementation of the mutant with a functional dps gene restored acid and hydrogen peroxide tolerance to levels equal to or greater than those exhibited by the parent strain. These results demonstrate that decreases in survival were from the absence of Dps or a protein regulated by Dps. The results from this study establish that Dps contributes to acid tolerance in E. coli O157:H7 and confirm the importance of Dps in oxidative stress protection.

Non-specific, general and multiple stress resistance of growth-restricted Bacillus subtilis cells by the expression of the sigmaB regulon.

Bacillus subtilis cells respond almost immediately to different stress conditions by increasing the production of general stress proteins (GSPs). The genes encoding the majority of the GSPs that are induced by heat, ethanol, salt stress or by starvation for glucose, oxygen or phosphate belong to the sigmaB-dependent general stress regulon. Despite a good understanding of the complex regulation of the activity of sigmaB and knowledge of a very large number of general stress genes controlled by sigmaB, first insights into the physiological role of this nonspecific stress response have been obtained only very recently. To explore the physiological role of this reguIon, we and others identified sigmaB-dependent general stress genes and compared the stress tolerance of wild-type cells with mutants lacking sigmaB or general stress proteins. The proteins encoded by sigmaB-dependent general stress genes can be divided into at least five functional groups that most probably provide growth-restricted B. subtilis cells with a multiple stress resistance in anticipation of future stress. In particular, sigB mutants are impaired in non-specific resistance to oxidative stress, which requires the sigmaB-dependent dps gene encoding a DNA-protecting protein. Protection against oxidative damage of membranes, proteins or DNA could be the most essential component of sigmaB mediated general stress resistance in growth-arrested aerobic gram-positive bacteria. Other general stress genes have both a sigmaB-dependent induction pathway and a second sigmaB-independent mechanism of stress induction, thereby partially compensating for a sigmaB deficiency in a sigB mutant. In contrast to sigB mutants, null mutations in genes encoding those proteins, such as cIpP or cIpC, cause extreme sensitivity to salt or heat.

Analysis of the decaprenyl diphosphate synthase (dps) gene in fission yeast suggests a role of ubiquinone as an antioxidant.

Schizosaccharomyces pombe produces ubiquinone-10 whose side chain is thought to be provided by the product generated by decaprenyl diphosphate synthase. To understand the mechanism of ubiquinone biosynthesis in S. pombe, we have cloned the gene encoding decaprenyl diphosphate synthase by the combination of PCR amplification of the fragment and subsequent library screening. The determined DNA sequence of the cloned gene, called dps, revealed that the dps gene encodes a 378-amino-acid protein that has the typical conserved regions observed in many polyprenyl diphosphate synthases. Computer-assisted homology search indicated that Dps is 45 and 33% identical with hexaprenyl diphosphate synthase from Saccharomyces cerevisiae and octaprenyl diphosphate synthase from Escherichia coli, respectively. An S. pombe dps-deficient strain was constructed. This disruptant was not able to synthesize ubiquinone and had no detectable decaprenyl diphosphate synthase activity, indicating that the dps gene is unique and responsible for ubiquinone biosynthesis. The S. pombe dps-deficient strain could not grow on either rich medium supplemented with glycerol or on minimal medium supplemented with glucose. The dps-deficient strain required cysteine or glutathione for full growth on the minimal medium. In addition, the dps-deficient strain is more sensitive to H2O2 and Cu2+ than the wild type. These results suggests a role of ubiquinone as an antioxidant in fission yeast cells.