Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

In the plasmid pUC8ksgA7, the coding region of the ksgA gene is preceded by the lac promoter (Plac) and a small open reading frame (ORF). This ORF of 15 codons is composed of nucleotides derived from the lacZ gene, a multiple cloning site and the ksgA gene itself. The reading frame begins with the ATG initiation codon of lacZ and ends a few nucleotides beyond the ATG start codon of ksgA. The ksgA gene is not preceded by a Shine-Dalgarno (SD) signal. Cells transformed with pUC8ksgA7 produce active methylase, the product of the ksgA gene. Introduction of an in-phase TAA stop codon in the small ORF abolishes methylase production in transformed cells. On the plasmid pUC8ksgA5, which contains the entire ksgA region, the promoter of the ksgA gene was found to reside in a 380 base pair Bgl1-Pvu2 restriction fragment, partly overlapping the ksgA gene, by two independent methods. Cloning of this fragment in front of the galK gene in plasmid pKO1 stimulates galactokinase activity in transformants and its insertion into the expression vector pKL203 makes beta-galactosidase synthesis independent of the presence of Plac. The sequence of the Bgl1-Pvu2 fragment was determined and a putative promoter sequence identified. An SD signal could not be distinguished at a proper distance upstream from the ksgA start codon. Instead, an ORF of 13 codons starting with ATG in tandem with an SD signal and ending 4 codons ahead of the ksgA gene was identified. This suggests that translation of the ORF is required for expression of the ksgA gene.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of the ksgA gene of Escherichia coli determining kasugamycin sensitivity. 312 46

The functionality of the Streptomyces lividans beta-galactosidase signal peptide to direct heterologous protein export was examined. The signal peptide plus eight amino acids of mature protein were sufficient to export not only a naturally exported protein, interleukin-1 beta, but also a naturally occurring cytoplasmic protein, Escherichia coli galactokinase. Interestingly, cells which expressed yet exported galactokinase were phenotypically Gal-. The potential use of the exported galactokinase system for the isolation and characterization of mutations within signal peptides and the export machinery of the host is discussed.
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PMID:Secretion of interleukin-1 beta and Escherichia coli galactokinase by Streptomyces lividans. 313 9

Two novel affinity tails, polycysteine and polyphenylalanine, have been genetically attached to galactokinase (EC 2.7.1.6) and beta-galactosidase (EC 3.2.1.23) in order to facilitate their purification. A chemically synthesized DNA linker encoding four cysteine residues was thus fused in frame with the galactokinase gene. The gene product, cysteine galactokinase, was significantly retarded on a column of thiopropyl-Sepharose. Using pulse elution, cysteine galactokinase was eluted at 10 mM DTT. Under the condition used, native galactokinase did not bind to thiopropyl-Sepharose. Homopolymer tailing was employed to prepare a phenylalanine-modified beta-galactosidase. One of the obtained genetic transformants coding for a beta-galactosidase carrying 11 phenylalanine residues at the N-terminus of the enzyme was isolated. With the aid of hydrophobic interaction chromatography the modified enzyme could be purified to homogeneity on fast protein liquid chromatography using a phenyl-Superose column.
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PMID:Enzyme purification by genetically attached polycysteine and polyphenylalanine affinity tails. 314 91

Transcription of SSA1 (formerly YG100), a member of the hsp70 gene family in Saccharomyces cerevisiae, increases dramatically upon heat shock. An expression vector in which the promoter of SSA1 is fused to the Escherichia coli galactokinase gene (galK) was constructed and transformed into a galactokinase-deficient yeast strain. The transformants grew on galactose at 23 degrees C, but increased expression of the SSA1-galK fusion gene inhibited growth of cells on galactose at 37 degrees C. Selection for survivors under nonpermissive conditions yielded a class of mutants, termed HSR (for heat shock regulation), which showed reduced levels of expression of the hsp70-galK gene fusion as determined by measurement of galactokinase activity. Similar effects on beta-galactosidase activity were obtained when an SSA1-lacZ fusion vector was introduced into the mutants, suggesting action in trans through the SSA1 promoter. Analysis of Northern (RNA) blots demonstrated that the reduction in expression was a result of decreased mRNA levels for the fusion gene. In addition, mRNA levels of the endogenous SSA1 gene are reduced in an HSR mutant. Genetic analysis has shown that these mutations act in trans and affect both transcription from the SSA1 promoter and turnover of the fusion transcript. These are the first trans-acting mutations known to affect directly the transcriptional regulation and transcript stability of heat shock genes in eucaryotes.
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PMID:Isolation of mutations that act in trans to alter expression from a yeast hsp70 promoter. 314 11

Paigen, Kenneth (Roswell Park Memorial Institute, Buffalo, N.Y.). Phenomenon of transient repression in Escherichia coli. J. Bacteriol. 91:1201-1209. 1966.-A family of mutants has been obtained in Escherichia coli K-12 in which beta-galactosidase is not inducible for approximately one cell generation after the cells are transferred to glucose from other carbon sources. After that period; the enzyme can be induced at the level appropriate to glucose-grown cultures of the parent cells. Among a wide variety of carbon sources, the only one capable of eliciting a state of transient repression is glucose. Conversely, transient repression occurs when cells are transferred to glucose from any of a variety of other carbon sources. The only exceptions to this so far discovered are lactose, gluconate, and xylose. Susceptibility to transient repression in mutants can also be induced in glucose-grown cells by a period of starvation. Mutant cells which have become susceptible to transient repression lose susceptibility in the presence of glucose only when they are under conditions which permit active protein synthesis. The presence of an inducer of beta-galactosidase is not required during this time, nor does pre-induction for beta-galactosidase diminish the susceptibility of mutants. At least two other catabolite repression-sensitive enzymes (galactokinase and tryptophanase) are also sensitive to transient repression, and the two phenomena are probably related. The absolute specificity of glucose and the pattern of response seen after growth in different carbon sources suggest that the endogenous metabolite which produces these repressions is far more readily derived from glucose in metabolism than it is from any other exogenous carbon source.
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PMID:Phenomenon of transient repression in Escherichia coli. 532 97

Loomis, William F., Jr. (Massachusetts Institute of Technology, Cambridge, Mass.), and Boris Magasanik. Nature of the effector of catabolite repression of beta-galactosidase in Escherichia coli. J. Bacteriol. 92:170-177. 1966.-Many carbon sources were found to give rise to catabolite repression of beta-galactosidase in a mutant strain of Escherichia coli lacking hexose phosphate isomerase activity. Compounds containing glucose or galactose cannot be formed from several of these carbon sources in this mutant strain, and, therefore, appear not to be required for catabolite repression of beta-galactosidase. Glucose was observed to elicit catabolite repression of beta-galactosidase in another mutant strain under conditions in which the formation of compounds of the citric acid cycle is inhibited. If catabolite repression of the lac operon is mediated by a single compound, it appears that the compound is related to the pentoses and trioses of intermediary metabolism. The repression of beta-galactosidase by galactose in galactokinase negative strains was shown to be independent of the gene, CR, which determines catabolite sensitivity of the lac operon, and to be dependent on a functional i gene.
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PMID:Nature of the effector of catabolite repression of beta-galactosidase in Escherichia coli. 532 48

We isolated and identified mutant strains of Kluyveromyces lactis that are defective for the Leloir pathway enzymes galactokinase, transferase, and epimerase, and we termed these loci GAL1 , GAL7 , and GAL10 , respectively. Genetic data indicate that these three genes are tightly linked, having an apparent order of GAL7 - GAL10 - GAL1 . This same gene order has been observed in Saccharomyces cerevisiae. Strains harboring gal7 mutations have elevated levels of beta-galactosidase, coded by an unlinked gene, galactokinase, and epimerase activities under uninduced conditions. We investigated the genetic basis of this constitutive gene expression and found no recombinants between the constitutive and Gal- phenotypes among 76 tetrads, suggesting that either GAL7 or a tightly linked gene codes for a regulatory function. This is the second gene that has been shown to specifically coregulate expression of the genes coding for beta-galactosidase and the Leloir pathway enzymes.
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PMID:Genetic and biochemical characterization of the galactose gene cluster in Kluyveromyces lactis. 632 19

We have previously presented evidence that rifampicin promotes readthrough of various transcriptional terminators in vivo. This conclusion was based on measurements of galactokinase or beta-galactosidase synthesis in Escherichia coli strains, harbouring plasmids having the terminators fused upstream of galK or lacZ respectively. The terminators tested did not include any known example of a fully rho-dependent signal. We now show that the drug does stimulate galactokinase production when galK is fused downstream of such a terminator: the first rightward terminator of lambda. We also show that the nusA1 host mutation affects neither termination nor the drug response at this site.
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PMID:Evidence for rifampicin-promoted readthrough of a fully rho-dependent transcriptional terminator. 642 35

The effects of the following pyrimidine nucleoside 5'-triphosphates: f5 UTP, br5 UTP, rTTP, s2 UTP, s4 UTP and s2 CTP on cell-free expression of the beta-galactosidase gene in lambda h80dlac DNA as well as the galactokinase gene in plasmid 01-14 were investigated. Only rTTP could substitute UTP in cell-free gene expression without restriction. Combinations of the other analogs with their respective natural congeners led to inhibition of gene expression. All analogs were found to inhibit transcription. Whereas br5 UTP and s4 UTP did not affect translation, mRNA containing s2 UMP or s2 CMP residues respectively was found to function poorly in translation. Only in the case of f5 UTP could ambiguitive behaviour be demonstrated. Whether mispairing of f5 UMP residues, responsible for this ambiguity takes place in transcription or in translation, could not be decided.
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PMID:The effect of nucleotide analogs on cell-free gene expression. 642 97

Three different Strep. salivarius (G2, G5 and G29) and two Strep. sanguis (GS3 and GS12) mutants affected in the phosphoenolpyruvate: glucose phosphotransferase system were selected on agar plates containing lactose and 2-deoxyglucose. All 5 were defective in a membrane-bound component of the transport system and grew less rapidly than the parent strain in 5 mM glucose-containing medium. Mutants G2 and G29 grew poorly in the presence of 5 mM mannose. Growth on mixed substrates revealed that the mutants and wild-type parents behaved differently. Wild-type strains in medium containing glucose plus another sugar (lactose, galactose, melibiose, raffinose or trehalose for Strep. salivarius and lactose, galactose or trehalose for Strep. sanguis) always exhausted most of the glucose before utilizing the other sugar. The mutants used the second sugar concurrently or preferentially to glucose. In medium containing glucose plus fructose or mannose, the wild types consumed both sugars concurrently whereas the mutants utilized the second sugar before glucose. Mutants G2 and G5 were insensitive to repression by fructose and released glucose into the medium when grown in the presence of 0.4 per cent lactose. Mutant G5 also released galactose. Sugar release was not detected with the wild types. The Strep. salivarius mutants contained normal levels of glucokinase and beta-galactosidase but G5 was almost totally devoid of galactokinase activity after growth on lactose. On galactose, the activity was restored. It seems that the phosphoenolpyruvate: glucose phosphotransferase system is involved in the regulation of sugar utilization in these two streptococci.
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PMID:Control of sugar utilization in the oral bacteria Streptococcus salivarius and Streptococcus sanguis by the phosphoenolpyruvate: glucose phosphotransferase system. 657 44


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