Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The principal iron uptake system of Saccharomyces cerevisiae utilizes a reductase activity that acts on ferric iron chelates external to the cell. The FRE1 gene product is required for this activity. The deduced amino acid sequence of the FRE1 protein exhibits hydrophobic regions compatible with transmembrane domains and has significant similarity to the sequence of the plasma membrane cytochrome b558 (the X-CGD protein), a critical component of a human phagocyte oxidoreductase, suggesting that FRE1 is a structural component of the yeast ferric reductase. FRE1 mRNA levels are repressed by iron. Fusion of 977 base pairs of FRE1 DNA upstream from the translation start site of an Escherichia coli lacZ reporter gene confers iron-dependent regulation on expression of beta-galactosidase in yeast. An 85-base-pair segment of FRE1 5' noncoding sequence contains a RAP1 binding site and a repeated sequence, TTTTTGCTCAYC; this segment is sufficient to confer iron-repressible transcriptional activity on heterologous downstream promoter elements.
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PMID:Ferric reductase of Saccharomyces cerevisiae: molecular characterization, role in iron uptake, and transcriptional control by iron. 157 Mar 6

In Saccharomyces cerevisiae, the COR2 gene codes for the 40 kDa subunit II of the QH2: cytochrome c oxidoreductase, an enzyme of the mitochondrial respiratory chain. Regions in the 5' flank of this gene important for regulated expression were identified by assaying beta-galactosidase activities in cells carrying different COR2-lacZ fusion genes. Sequences downstream of position -201 relative to the translational initiation codon are sufficient to confer regulation by carbon source, whereas sequences downstream of position -153 do not give rise to significant expression. A binding site for the abundant general transcription factor GFI is present in the region between -201 and -153 just upstream from sequences which resemble the consensus DNA recognition sequence of the regulatory protein complex HAP2/HAP3: 5'-TNATTGGT-3'. By quantitating RNA levels and assaying beta-galactosidase activities we show that synthesis of COR2, which is not a hemoprotein, is regulated by HAP1, HAP2/HAP3 and heme.
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PMID:Expression of the gene encoding subunit II of yeast QH2: cytochrome c oxidoreductase is regulated by multiple factors. 216 71

Sepiapterin reductase (7,8-dihydrobiopterin: NADP+ oxidoreductase, EC 1.1.1.153) catalyzes the terminal step in the biosynthetic pathway for tetrahydrobiopterin, the cofactor necessary for aromatic amino acid hydroxylation. We report here the isolation of a cDNA clone for rat liver sepiapterin reductase. The cDNA has been excised from a lambda vector and the DNA sequence was determined. The insert contains the coding sequence for at least 95% of the rat enzyme and is fused to the Escherichia coli beta-galactosidase N-terminal segment and the lac promoter. The N-terminal region of the clone contains an extraordinarily high G + C content. The amino acid sequence deduced from the clone is in agreement with the size and composition of the enzyme and was matched to several tryptic peptide sequences. The enzyme encoded by the cDNA insert was shown to have sepiapterin reductase activity after expression in E. coli. Structural similarities were identified between this protein and several enzymes that should contain similar nucleotide and pteridine binding sites.
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PMID:Isolation and expression of rat liver sepiapterin reductase cDNA. 220 Oct 30

A gene of the chloroplast genome has been designated the psbG gene on the basis that in maize the gene product is a 24-kDa polypeptide of photosystem two (PS2) (Steinmetz, A. A., Castroviejo, M., Sayre, R. T., and Bogorad, L. (1986) J. Biol. Chem. 261, 2485-2488). We have located and sequenced the equivalent gene in wheat (Triticum aestivum) and have raised specific antibodies to the gene product following its expression in Escherichia coli as a beta-galactosidase fusion protein. Using these antibodies, we have investigated the location of the gene product in various thylakoid membrane fractions of pea (Pisum sativum). The gene product of apparent molecular mass 27-28 kDa is severely depleted in PS2-enriched membrane preparations and its distribution between stromal and granal regions of the membrane is distinct to that of the psbC gene product which is known to be a core polypeptide of PS2. We therefore conclude that psbG does not code for a component of PS2 but instead suggest that it is present in a novel protein complex of the thylakoid membrane. On the basis of 1) the conserved overlap between psbG and ndhC, a chloroplast gene which shows significant homology to a mitochondrial gene that codes for a subunit of the NADH-ubiquinone oxidoreductase of mitochondria, and 2) sequence similarity between the psbG gene product and the ndh gene product of E. coli, which codes for a respiratory NADH dehydrogenase, we propose that this ill-defined complex functions as a NADH or NADPH-plastoquinone oxidoreductase.
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PMID:psbG is not a photosystem two gene but may be an ndh gene. 266 82

The Mu dl (ApR lac) bacteriophage was used to generate mutants of Escherichia coli which were defective in formate hydrogenlyase. Three mutants were chosen for further analysis: they lacked hydrogenase (hydrogen: benzyl viologen oxidoreductase) activity, but produced normal levels of fumarate reductase activity and two- to three-fold reduced levels of benzyl viologen (BV)-dependent formate dehydrogenase activity. Two of them (hydC) were shown to contain about 4-fold reduced amounts of formate hydrogenlyase and fumarate-dependent H2 uptake activities. The third one (hydD) was totally devoid of both activities. Their insertion sites were located at 77 min on the E. coli map. Subdivision of these mutants into two classes was subsequently based on the restoration capacity of hydrogenase activity with high concentration of nickel in the growth media. Addition of 500 microM NiCl2 led to a complete recovery of hydrogenase activity, and to the concomitant restoration of normal BV-linked formate dehydrogenase, formate hydrogenlyase and fumarate-dependent H2 uptake activities in the hydC mutants. The hydD mutant was insensitive to the effect of nickel. Expression of the lac operon in hydC and hydD mutants was induced by anaerobiosis. It was not increased by the addition of formate under anaerobic conditions. The presence of nitrate resulted in slightly reduced beta-galactosidase activities in the hydC mutants, whereas those found in the hydD mutant reached only one third of the level obtained in its absence. Fumarate had no effect on both classes. Moreover, in contrast to the hydD locus, the hydC::Mu dl fusions were found to be dependent upon the positive control exerted by the nirR gene product and were totally repressed by an excess of nickel. In addition, the low levels of overall hydrogenase-dependent activities found in a nirR strain were also relieved by the presence of nickel. Our results strongly suggest that the pleiotropic regulatory gene nirR is essential for the expression of a gene (hydC) involved in either transport or processing of nickel in the cell, whose alteration leads to a loss of hydrogenase activity.
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PMID:Genetic and physiological characterization of new Escherichia coli mutants impaired in hydrogenase activity. 308 8

Mutants of Erwinia chrysanthemi impaired in pectin degradation were isolated by chemical and Mu d(Ap lac) insertion mutagenesis. A mutation in the kduD gene coding for 2-keto-3-deoxygluconate oxidoreductase prevented the growth of the bacteria on polygalacturonate as the sole carbon source. Analysis of the kduD::Mu d(Ap lac) insertions indicated that kduD is either an isolated gene or the last gene of a polycistronic operon. Some of the Mu d(Ap lac) insertions were kduD-lac fusions in which beta-galactosidase synthesis reflected kduD gene expression. In all these fusions, beta-galactosidase activity was shown to be sensitive to catabolite repression by glucose and to be inducible by polygalacturonate, galacturonate, and other intermediates of polygalacturonate catabolism. Galacturonate-mediated induction was prevented by a mutation which blocked its metabolism to 2-keto-3-deoxygluconate. 2-Keto-3-deoxygluconate appeared to be the true inducer of kduD expression resulting from galacturonate degradation. 5-Keto-4-deoxyuronate or 2,5-diketo-3-deoxygluconate were the true inducers, originating from polygalacturonate cleavage. These three intermediates also appeared to induce pectate lyases, oligogalacturonate lyase, and 5-keto-4-deoxyuronate isomerase synthesis.
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PMID:Isolation of Erwinia chrysanthemi kduD mutants altered in pectin degradation. 394 17

In order to relate the biogenesis of the lactose transport system to lipid synthesis, a glycerol-requiring mutant of Escherichia coli K-12 with a specific defect in l-glycerol-3-phosphate synthesis was isolated and characterized. The defective enzyme is the biosynthetic l-glycerol-3-phosphate dehydrogenase [l-glycerol-3-phosphate: NAD (P) oxidoreductase, EC 1.1.1.8] which functions as a dihydroxyacetone phosphate reductase to provide l-glycerol-3-phosphate for lipid synthesis. In this mutant, removal of glycerol from the growth medium results in inhibition of the synthesis of protein, deoxyribonucleic acid, and phospholipid. Inhibition of phospholipid synthesis immediately follows glycerol removal, whereas the inhibition of deoxyribonucleic acid and protein synthesis is preceded by a short lag period. Glycerol starvation does not change the turnover pattern of previously synthesized phospholipids. The blocking of lipid synthesis by glycerol starvation causes a drastic decrease in inducibility of beta-galactoside transport activity relative to beta-galactosidase, indicating that induction of lactose transport requires de novo lipid synthesis.
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PMID:Induction of the lactose transport system in a lipid-synthesis-defective mutant of Escherichia coli. 491 67

Escherichia coli K12 growing anaerobically on L-fucose excretes L-1,2-propanediol as a fermentation product whose formation is catalysed by an inducible NAD-linked oxidoreductase. The activity of this enzyme is highly induced only during anaerobic growth. Three bacterial strains bearing a hybrid operon with the structural genes for lactose utilization (lacZYA) fused to the promoter of the propanediol oxidoreductase gene (fucO) were constructed to test whether or not transcriptional control was involved. In contrast to propanediol oxidoreductase of wild-type cells, beta-galactosidase in the phi(fuc-lac) strains was induced by fucose to high levels both aerobically and anaerobically. Data from this work are in accord with the previous report that the enzyme protein (assayed by specific antibodies) was induced both aerobically and anaerobically, but that only in anaerobically grown cells was the oxidoreductase catalytically active. In the present study, we found that the oxidoreductase induced anaerobically in wild-type cells remained enzymically active during aerobic growth in the absence of fucose. On the other hand, wild-type cells grown aerobically in the presence of fucose and then allowed limited anaerobic growth on glucose did not gain any oxidoreductase activity. The mechanism of this post-transcriptional control remains to be discovered.
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PMID:Use of operon fusions to examine the regulation of the L-1,2-propanediol oxidoreductase gene of the fucose system in Escherichia coli K12. 631 47

None of the Agrobacterium tumefaciens and A. rubi strains tested produces detectable amounts of beta-galactosidase although they are capable of utilizing lactose as sole source of carbon. This opportunity was taken to investigate the expression of lac transposon Tn951 (Cornelis et al. 1978) in Agrobacterium with the ultimate goal of using this system to investigate alien gene expression. When the transposon was introduced with the help of a broad-host range plasmid, RP1, the transconjugants produced significant quantities of beta-galactosidase which was inducible by isopropyl-beta-D-thiogalactopyranoside. Tn951 was capable of restoring the Lac+ phenotype to an A. tumefaciens mutant not capable of using lactose. Cellobiose, a known inducer of aldohexopyranoside: cytochrome c oxidoreductase (which regulates the characteristic 3-ketolactose production in Agrobacterium; van Beeumen and De Ley (1968), had no effect on beta-galactosidase activity.
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PMID:Studies on Tn951 (lac+) expression in Agrobacterium. 632 25

During anaerobic growth on L-fucose, Escherichia coli excretes L-1,2-propanediol formed by an inducible NAD-linked oxidoreductase. The activity of this enzyme is highly induced by L-fucose only anaerobically. However, in strains bearing a hybrid operon with the promoter of fucO (the propanediol oxidoreductase gene) fused to lacZYA, the beta-galactosidase activity is inducible by fucose both anaerobically and aerobically. In merodiploids bearing both fucO+ and phi(fucO-lac), propanediol oxidoreductase is inducible only anaerobically, but beta-galactosidase remains inducible both aerobically and anaerobically. Thus, the absence of respiratory control in the expression of phi(fucO-lac) cannot be attributed to a polarity effect of the fusion on a gene encoding a protein with autogenous regulatory function in transcription. The respiratory effect on the induced propanediol oxidoreductase activity is therefore post-transcriptional.
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PMID:Post-transcriptional control of L-1,2-propanediol oxidoreductase in the L-fucose pathway of Escherichia coli K-12. 641 21


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