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)

We describe cir-lac operon fusions constructed by using phage Mu d(Apr lac). Expression of beta-galactosidase in these fusion strains is analogous to known regulatory properties of cir gene expression. It is concluded that the observed regulation by iron of the cir gene is under transcriptional control.
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PMID:Use of cir-lac operon fusions to study transcriptional regulation of the colicin Ia receptor in Escherichia coli K-12. 700 29

The lac genes were inserted with phage Mu(Ap, lac) into the fhuA, fepA, cir and tonB genes which specify components of iron uptake systems. The expression of lac in all these operon fusions was controlled by the availability of iron to the cells, thereby facilitating a quick and simple measurement of the expression of the genes listed above. In an iron rich medium under anaerobic conditions all systems were strongly repressed. fhuA was depressed at higher iron concentration than was fepA or cir, and tonB was repressed only under anaerobic conditions and could be induced by iron limitation. Mutants constitutive for the expression of beta-galactosidase were selected in a fhuA-lac fusion strain. The outer membrane proteins Cir, FhuA, FecA, 76K and 83K were made constitutively in such mutant strains. Therefore, they were termed fur mutants. In these fur mutant strains, the synthesis of a 19K protein was reduced. Furthermore, it was found that transport of ferric enterochelin and ferrichrome was also constitutive in the fur mutant cells, and that ferric citrate uptake could be induced by only 10 microM citrate in the growth medium in contrast to wild-type cells in which at least 100 microM citrate was necessary. The fepA gene was concluded to be under an additional control, because it was not fully derepressed by the fur mutation.
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PMID:Regulation of ferric iron transport in Escherichia coli K12: isolation of a constitutive mutant. 702 76

Actinobacillus actinomycetemcomitans (A.a.) can produce a potent leukotoxin that is thought to be involved in evasion of the host immune response. In order to understand the role of A.a. and its leukotoxin in the initiation and progression of periodontal disease, it is important determine how the expression of A.a. virulence factors might be regulated by the local periodontal micro-environment. To facilitate the measurement of leukotoxin levels, a leukotoxin-beta-galactosidase gene fusion was constructed and recombined into the chromosome of A.a. strain JP2 at the leukotoxin locus. The resulting strain, AAM17, produces beta-galactosidase under control of the leukotoxin promoter. It also produces leukotoxin, since integration of the gene fusion into the chromosome was designed to produce a duplication of the leukotoxin gene. This strain was used to measure the change in leukotoxin level in response to alterations in two environmental signals: iron concentration and oxygen tension. When AAM17 was grown in iron-limited media that did not alter growth rate but did increase the levels of other iron-regulated proteins, the levels of the leukotoxin-beta-galactosidase were similar to those found in AAM17 grown in iron-replete media. These results were confirmed in strains AAM17 and JP2 by leukotoxicity assays and RNA blots. Aerobic growth of AAM17 resulted in a three-fold decrease in leukotoxin beta-galactosidase activity compared with anaerobically grown cells. These results indicate that the A.a. leukotoxin is regulated by some of the environmental signals that may vary in the gingival crevice.
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PMID:The regulation of leukotoxin production in Actinobacillus actinomycetemcomitans strain JP2. 766 14

Vibrio vulnificus infections have been associated with iron overload and preexisting liver disease. Iron may play a major role in the pathogenesis of V. vulnificus infections. Many virulence genes, as well as genes involved in the transport of iron by bacteria, are regulated by iron, with increased expression under low-iron conditions. In Escherichia coli and Vibrio cholerae, transcriptional regulation by iron depends on the fur gene. We utilized Southern hybridization under low- and high-stringency conditions with both E. coli and V. cholerae fur gene probes to demonstrate that there are fur-homologous sequences in the DNAs of V. vulnificus, Vibrio fischeri, and Aeromonas sp. but not in the DNAs of the other bacterial species tested. We developed a restriction map and cloned the fur-homologous sequence from V. vulnificus. The hybridizing clone of V. vulnificus chromosomal DNA complemented a V. cholerae fur mutant. DNA sequence analysis confirmed the presence of a 149-amino-acid open reading frame that was 77% homologous to E. coli Fur and 93% homologous to V. cholerae Fur. Primer extension localized a single promoter for the V. vulnificus fur gene. Northern (RNA) blot analysis and beta-galactosidase assays of an operon fusion to lacZ suggested that there was not significant regulation of transcription of V. vulnificus fur by iron or the E. coli Fur protein. We used marker exchange to construct a V. vulnificus fur deletion mutant and confirmed its phenotype by observing overexpression of iron-regulated outer membrane proteins on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The fur deletion mutant of V. vulnificus will be helpful in future studies of the role of iron in V. vulnificus pathogenesis.
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PMID:Cloning and genetic analysis of the Vibrio vulnificus fur gene and construction of a fur mutant by in vivo marker exchange. 767 93

Pseudomonas aeruginosa PAO was mutagenized with Tn1737KH, a type I transcription probe transposon containing a promoterless lacZ (beta-galactosidase) gene, and 24 insertion mutants that did not grow under iron-deficient conditions were isolated. None of the culture supernatants from any mutants contained pyoverdin, a low-molecular-weight siderophore able to sequester ferric iron at very high affinity, and the growth defects of the mutants were all phenotypically recovered by the addition of the culture supernatant from the wild-type strain. These phenotypes led to the inference that all the mutants had defects in the genes (pvd genes) for production of pyoverdin. In some pvd::Tn1737KH mutants, high levels of beta-galactosidase activities were observed, and such activities were drastically reduced by the addition of ferric ion in the culture media, indicating that the expression of at least some pvd genes is regulated at the transcriptional level. Molecular cloning and physical analysis of the chromosomal fragments with Tn1737KH insertions allowed us to allocate all the mutations within a 103-kb region, referred to as the pvd region, that was found to locate at 47 min on the genetic map of PAO. Further physical mapping and Southern analysis showed that there is a 10-kb overlap between the pvd region and the 125-kb catA region described by Zhang and Holloway (C. Zhang and B. W. Holloway, J. Gen. Microbiol. 138:1097-1107, 1992). We could hence illustrate the physical map of the P. aeruginosa chromosome with a size of 218 kb.
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PMID:Genetic and physical mapping of genes involved in pyoverdin production in Pseudomonas aeruginosa PAO. 781 32

A homolog of the Corynebacterium diphtheriae dtxR gene was isolated from Brevibacterium lactofermentum. The product of the B. lactofermentum dtxR gene was immunoreactive with polyclonal anti-DtxR antibodies and functioned as an iron-activated repressor capable of regulating the expression of beta-galactosidase from a diphtheria tox promoter/operator transcriptional fusion in recombinant Escherichia coli. The extents of induction by increasing concentrations of the chelator 2,2'-dipyridyl were identical in cells expressing DtxR from either C. diphtheriae or B. lactofermentum.
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PMID:Molecular cloning, DNA sequence analysis, and characterization of the Corynebacterium diphtheriae dtxR homolog from Brevibacterium lactofermentum. 781 38

A Yersinia pestis fur mutation was constructed by insertionally disrupting the fur open reading frame. Analysis of a Fur-regulated beta-galactosidase reporter gene revealed a loss of iron regulation as a result of the fur mutation. trans complementation with the cloned Y. pestis fur gene restored iron regulation. The expression of most iron-regulated proteins was also deregulated by this mutation; however, a number of iron-repressible and two iron-inducible polypeptides retained normal regulation. Mutations in fur or hmsH, a gene encoding an 86-kDa surface protein required for hemin storage, increased the sensitivity of Y. pestis cells to the bacteriocin pesticin. Interestingly, the Y. pestis fur mutant lost temperature control of hemin storage; however, expression of the HmsH polypeptide was not deregulated. When grown with excess iron, a Y. pestis fur mutant possessing the 102-kb pigmentation locus exhibited severe growth inhibition and a dramatic increase in the number of spontaneous nonpigmented chromosomal deletion mutants present at late log phase. These results suggest that the Fur protein of Y. pestis is an important global regulator and that a separate Fur-independent iron regulatory system may exist.
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PMID:Pleiotropic effects of a Yersinia pestis fur mutation. 800 85

In Pseudomonas aeruginosa, production of exotoxin A, an ADP-ribosyltransferase, is a complex and highly regulated process. Two positively acting regulatory genes, regA and regB, have been cloned and characterized. To identify additional exotoxin A regulatory genes, we have characterized four N-methyl-N'-nitro-N-nitrosoguanidine-generated mutants of P. aeruginosa PA103 which are deficient in exotoxin A production. These mutants (PA103-8, PA103-15, PA103-16, and PA103-19) do not accumulate intracellular exotoxin A and are not complemented by the cloned toxA or regAB genes. This observation indicates that the lesion(s) in the mutants is probably in an exotoxin A regulatory gene(s) and is not in the genes for secretion of exotoxin A or in the toxA or regAB genes. To assess the effect of the putative regulatory mutations on the toxA and regAB genes, we compared the activity of the toxA and regAB promoters in the mutant and parental strains using plasmids containing the genes for beta-galactosidase or chloramphenicol acetyltransferase under the control of either the toxA or the regAB promoter. The toxA promoter-beta-galactosidase fusion plasmid could not be maintained in PA103-8. beta-Galactosidase expression driven by the toxA promoter was absent in the mutant PA103-19 and occurred at a low level, which was not repressed by iron in mutants PA103-15 and PA103-16. The regAB genes are temporally controlled by two promoters, P1 and P2. In all four mutants, regAB P1 promoter activity was reduced; however, expression under the control of the regAB P2 promoter was normal. These observations suggest the existence of one or more regulatory genes which directly affect expression of both the toxA and the regAB P1 promoters.
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PMID:Characterization of Pseudomonas aeruginosa mutants that are deficient in exotoxin A synthesis and are altered in expression of regA, a positive regulator of exotoxin A. 811 61

The use of copper, zinc, iron, nickel and calcium in three different chelating gels was investigated for preparing immobilized beta-galactosidase. The chelated ligands [Cu(2+)-iminodiacetate (IDA), Cu(2+)-Tris(carboxymethyl)ethylenediamine (TED), Ni(2+)-IDA and Fe(3+)-IDA] absorbed the protein so strongly that it can be considered a true immobilization. The obtained enzyme derivatives were investigated with regard to activity and stability. Enzymic activity was highly preserved in general for the TED derivates (90% when compared with that for Cu(2+)-TED). The immobilized Ni2+ derivatives were more stable to high temperature and to storage than the Cu2+ derivatives. Temperature-stability of the immobilized enzyme was very much improved by adding a strong metal-chelating gel such as carboxymethylated tetraethylenepentamine-agarose. The gel could be re-used and reloaded after elution with chelator. beta-Galactosidase from Escherichia coli was purified using immobilized-metal-ion-chelate chromatography (i.m.a.c.). The potential use of beta-galactosidase immobilized on i.m.a.c. gels for technical purposes is discussed.
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PMID:Immobilization of beta-galactosidase on metal-chelate-substituted gels. 819 68

The regulation of hutA, the Vibrio cholerae gene encoding a 77-kDa iron-regulated outer membrane protein required for heme iron utilization, was characterized, and the DNA sequence of the gene was determined. A hutA::Tn5 lac fusion generated previously (D. P. Henderson and S. M. Payne, Mol. Microbiol. 7:461-469, 1993) was transformed into Fur- and Fur+ strains of Escherichia coli and V. cholerae. The results of beta-galactosidase assays on the transformed strains demonstrated that transcription of hutA is regulated by the Fur repressor protein in E. coli and at least partially regulated by Fur in V. cholerae. Analysis of the DNA sequence of hutA indicated that a sequence homologous to the E. coli consensus Fur box was present in the promoter region of hutA. The amino acid sequence of HutA is homologous to those of several TonB-dependent outer member proteins. However, when the V. cholerae heme utilization system, which requires one or more genes encoded by the recombinant plasmid pHUT10 in addition to hutA carried on a second vector, was transferred to a wild-type strain and an isogenic tonB mutant of E. coli, the tonB mutant could utilize heme iron as efficiently as the wild-type strain. These data indicate that the V. cholerae heme utilization system reconstituted in E. coli does not require a functional TonB protein. The tonB mutant transformed with the heme utilization plasmids could not utilize the siderophore ferrichrome as an iron source, indicating that none of the genes encoded on the heme utilization plasmids complements the tonB defect in E. coli. It is possible that a gene(s) encoded by the recombinant heme utilization plasmids encodes a protein serving a TonB-like function in V. cholerae. A region in the carboxy terminus of HutA is homologous to the horse hemoglobin gamma chain, and the amino acids involved in forming the heme pocket in the gamma chain are conserved in HutA. These data suggest that this region of HutA is involved in heme binding.
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PMID:Characterization of the Vibrio cholerae outer membrane heme transport protein HutA: sequence of the gene, regulation of expression, and homology to the family of TonB-dependent proteins. 819 82


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