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)

Gene fusions between the lac structural genes and various genes of the hexuronate system of Escherichia coli K12 were isolated by the technique of Casadaban. Mud(Aprlac) and lambda plac-Mu insertion mutants were constructed in which the lac genes were fused to the regulatory region of the uxu operon. In all the uxu-lac fusion strains, beta-galactosidase expression was shown to be inducible by the natural inducers of the uxu operon (glucuronate and fructuronate) and sensitive to catabolite repression by glucose. In addition we isolated a Mud(Aprlac) fusion where the lac genes were fused to the uxuR regulatory gene. In this fusion the synthesis of beta-galactosidase reflects the regulation of the uxuR gene. In the presence of a wild-type uxuR allele, partial repression of beta-galactosidase expression was found; the repression was removed when inducer was added. This result indicates that while the uxuR gene is subject to autogenous control, the uxuR repressor may have only a low affinity for its own operator.
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PMID:Regulation of expression of the uxu operon and of the uxuR regulatory gene in Escherichia coli K12. 642 May 8

Wild-type ebg enzyme, the second beta-galactosidase of Escherichia coli K12, does not permit growth on lactose. As part of a study of the evolution of new enzymatic functions, I have selected, from a lacZ deletion strain, a variety of spontaneous mutants that grow on lactose and other beta-galactoside sugars. Single point mutations in the structural gene ebgA alter the enzyme so that it hydrolyzes lactose or lactulose effectively; two mutations in ebgA permit galactosylarabinose hydrolysis, while three mutations are required for lactobionic acid hydrolysis. Wild-type ebg enzyme and 16 functional mutant ebg enzymes were purified and analyzed kinetically to determine how the substrate specificities had changed during the directed evolution of these new functions. The specificities for the biologically selected substrates generally increased by at least an order of magnitude via increased Vmax and decreased Km for the substrate. These changes were very specific for the selected substrate, often being accompanied by decreased specificities for other related substrates. The single, double, or triple substitutions in the enzymes did not detectably alter the thermal stability of ebg enzyme.
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PMID:Changes in the substrate specificities of an enzyme during directed evolution of new functions. 679 63

A new mutation in Escherichia coli K12, isfA, is described, which causes inhibition of SOS functions. The mutation, discovered in a delta polA+ mutant, is responsible for inhibition of several phenomena related to the SOS response in polA+ strains: UV- and methyl methanesulfonate-induced mutagenesis, resumption of DNA replication in UV-irradiated cells, cell filamentation, prophage induction and increase in UV sensitivity. The isfA mutation also significantly reduces UV-induced expression of beta-galactosidase from recA::lacZ and umuC'::lacZ fusions. The results suggest that the isfA gene product may affect RecA* coprotease activity and may be involved in the regulation of the termination of the SOS response after completion of DNA repair. The isfA mutation was localized at 85 min on the E. coli chromosome, and preliminary experiments suggest that it may be dominant to the wild-type allele.
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PMID:A new mutation in Escherichia coli K12, isfA, which is responsible for inhibition of SOS functions. 765 21

The periplasmic enzyme beta-lactamase was selectively released from Escherichia coli K12 by the amphiphilic quaternary ammonium compound tetradecyl betainate at certain concentration intervals. At low concentrations little enzyme was released, and at high concentrations enzyme inactivation occurred. Greater effects of tetradecyl betainate were seen both with respect to release and inactivation at higher pH. At intermediate concentrations of tetradecyl betainate high yields of beta-lactamase were obtained with no detectable contribution of the cytoplasmic marker beta-galactosidase. The highest yields of beta-lactamase activity were obtained when high concentrations of salt were added 1 min after permeation of the bacteria with tetradecyl betainate.
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PMID:Selective release of the periplasmic enzyme beta-lactamase from Escherichia coli with tetradecyl betainate. 803 73

The decay rate of the potential to synthesize proteins after complete inhibition of transcription by rifampicin was analyzed to determine the functional mRNA stability of exponentially growing and glucose-starved Escherichia coli B and K12 cells. We found the following: (i) The half-life of the mRNA pool increased 2.2-fold during a period of 2 h of starvation (from 1.8 min in exponentially growing cells to 4.0 min for cells starved for 2 h); (ii) the effect on transcript stability appeared to be global since transcripts of genes that were induced, repressed or unaltered in their expression during starvation exhibited more or less the same increased stability; (iii) the rate of peptide chain elongation, as measured by the synthesis time for beta-galactosidase, decreased 1.9-fold during the starvation period studied and may, at least in part, account for the global stabilization of transcripts in starved cells.
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PMID:Effects of starvation for exogenous carbon on functional mRNA stability and rate of peptide chain elongation in Escherichia coli. 818 21

The mutagenic consequences of covalent adducts induced in M13mp19 DNA by 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) and UVA have been determined in a forward mutational system capable of detecting all classes of mutagenic events. The photoreaction mediated by HMT has been carried out at a very low molar ratio of HMT to DNA which favours the induction of cross-links between high affinity reaction sites. When damaged M13mp19 DNA is used to transfect competent Escherichia coli K12 JM105 cells, a five-fold increase in mutation frequency is observed at 3.5% survivors when measured as a loss of beta-galactosidase alpha-complementation. The enhanced mutation frequency is largely due to base substitutions, frameshift events and large deletions. The single nucleotide substitutions occur both in the lac Z coding sequence and in its regulatory region. Transversion and transition have been detected with a predominant form consisting of A.T-to-G.C transversion at position +159. Frameshift mutations have been observed at five positions while three large deletions removing either part of the coding sequence or both the coding and the regulatory regions have been detected with a higher frequency. The spectrum of base substitutions detected between the M13 lac Z- phages surviving to the treatment is totally different from those appearing spontaneously whereas several frameshift events or deletions can already be detected between the spontaneous mutations. Despite the presence of these spontaneous hot spots, the spectrum of mutations recovered after HMT photoaddition appears to be unique and a detailed analysis of the different classes of mutations indicates an important role of cross-links in the production of mutations.
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PMID:Analysis of mutations induced by 4'-hydroxymethyl-4,5',8-trimethylpsoralen and UVA in Escherichia coli lac Z gene and its regulatory region. 827 Nov 15

We report the identification of Integration Host Factor (IHF) as a new element involved in modulation of P1, the upstream pyrimidine-specific promoter of the Escherichia coli K12 and Salmonella typhimurium carAB operons. Band-shift assays, performed with S-30 extracts of the wild type and a himA, hip double mutant or with purified IHF demonstrate that, in vitro, this factor binds to a region 300 bp upstream of the transcription initiation site of P1 in both organisms. This was confirmed by deletion analysis of the target site. DNase I, hydroxyl radical and dimethylsulphate footprinting experiments allowed us to allocate the IHF binding site to a 38 bp, highly A+T-rich stretch, centred around nucleotide -305 upstream of the transcription initiation site. Protein-DNA contacts are apparently spread over a large number of bases and are mainly located in the minor groove of the helix. Measurements of carbamoyl-phosphate synthetase (CPSase) and beta-galactosidase specific activities from car-lacZ fusion constructs of wild type or IHF target site mutants introduced into several genetic backgrounds affected in the himA gene or in the pyrimidine-mediated control of P1 (carP6 or pyrH+/-), or in both, indicate that, in vivo, IHF influences P1 activity as well as its control by pyrimidines. IHF stimulates P1 promoter activity in minimal medium, but increases the repressibility of this promoter by pyrimidines. These antagonistic effects result in a two- to threefold reduction in the repressibility of promoter P1 by pyrimidines in the absence of IHF binding. IHF thus appears to be required for maximal expression as well as for establishment of full repression. IHF could exert this function by modulating the binding of a pyrimidine-specific regulatory molecule.
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PMID:Integration host factor (IHF) modulates the expression of the pyrimidine-specific promoter of the carAB operons of Escherichia coli K12 and Salmonella typhimurium LT2. 845 62

In an ompF'-'lacZ fusion system carried by the open reading frame vector pORF1 in a supE mutant of Escherichia coli K12, read-through of an amber codon was decreased at temperatures higher than 40 degrees C. This effect of temperature was dependent on the nucleotide sequence surrounding the amber codon, which was inserted into a site between the ompF and lacZ cistrons. Upon a temperature shift-up from 30 to 42 degrees C, beta-galactosidase synthesis directed by this fusion showed a transient arrest.
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PMID:Temperature-sensitive amber suppression of ompF'-'lacZ fused gene expression in a supE mutant of Escherichia coli K12. 846 2

Mutants without pseudo-HPr activity intrinsic to the H domain of the FruB protein were obtained in Escherichia coli K12 through insertional mutagenesis by means of the MudIlac phage and TnPhoA transposon. For isolating these mutants, double mutants of enteric bacterium (ptsH fruR of ptsH fruS) were used as original strains. These double mutants were inactive with respect to the total HPr protein of the phosphoenolpyruvate-carbohydrate phosphotransferase system and could not provide constitutive synthesis of fructose-specific proteins of this system. The mutants obtained were designated fruH, mapped, and genetically characterized. Insertions were shown to be located in exactly the portion of the fruB gene that specifies synthesis of the H domain of the FruB protein. The fruH mutations decreased motility of bacterial both in a medium free of carbohydrates and in a medium with glucose, fructose, or maltose. In addition, fruH mutants with the MudIlac genome insertion had sharply decreased activity of beta-galactosidase.
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PMID:[Isolation and properties of mutants devoid of pseudo-HPr activity of the fructose transfer system in Escherichia coli K12]. 924 62

Escherichia coli K12 strains lysogenic for Mu gem2ts with the prophage inserted in a target gene (i.e., lacZ::Mu gem2ts lysogenic strains) revert to Lac+ by prophage precise excision with a relatively high frequency (about 1 x 10(-6)). The revertants obtained are still lysogens with the prophage inserted elsewhere in the bacterial chromosome. We have observed that, with the time of storage in stabs, bacterial cultures lysogenic for Mu gem2ts lose the ability to excise the prophage. The mutation responsible for this effect was co-transducible with the gyrB gene. After the removal of the prophage by P1 vir transduction from these strains, one randomly chosen clone, R3538, was further analyzed. It shows an increment of DNA supercoiling of plasmid pAT153, used as a reporter, and a reduced beta-galactosidase activity. On the other hand, R3538 is totally permissive to both lytic and lysogenic cycles of bacteriophage Mu.
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PMID:A spontaneous Escherichia coli K12 mutant which inhibits the excision-reintegration process of Mu gem2ts. 929 21


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