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)

Transcription of the trp operon of Bacillus subtilis is regulated by attenuation. A trpE'-'lacZ gene fusion preceded by the wild-type trp promoter-leader region was used to analyze regulation. Overproduction of the trp leader transcript in trans from a multicopy plasmid caused constitutive expression of the chromosomal trpE'-'lacZ fusion, presumably by titrating a negative regulatory factor encoded by the mtr locus. Subsegments of the trp leader region cloned onto the multicopy plasmid were examined for their abilities to elevate beta-galactosidase activity. An RNA segment spanning the portion of the leader transcript that forms the promoter-proximal strand of the proposed antiterminator structure was most active in this trans test. The data suggest that the mtr gene product, when activated by tryptophan, binds to this RNA segment and prevents formation of the antiterminator. In this manner, the trans-acting factor promotes formation of the RNA structure that causes transcription termination. Secondary-structure predictions for the leader segment of the trp operon transcript suggest that if the mtr factor bound this RNA segment in a nonterminated transcript, the ribosome-binding site for the first structural gene, trpE, could be sequestered in a stable RNA structure. We tested this possibility by comparing transcriptional and translational fusions containing the initial segments of the trp operon. Our findings suggest that the mtr product causes both transcription attenuation and inhibition of translation of trpE mRNA. Inhibition of translation initiation would reduce ribosome density on trpE mRNA, perhaps making it more labile. Consistent with this interpretation, the addition of tryptophan to mtr+ cultures increased the rate of trpE'-'lacZ mRNA decay.
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PMID:cis-acting sites in the transcript of the Bacillus subtilis trp operon regulate expression of the operon. 313 60

Tryptophan induces a rapid stimulation of polyribosomal aggregation and protein synthesis in the livers of rats or mice. This stimulatory effect of tryptophan correlates with increased levels of mRNA in the cytoplasm of the liver and is related to enhanced translocation of nuclear mRNA into the cytoplasm. In the present study the possible role of glycoproteins of the rat liver, particularly those in the nuclear membranes and in the cytosol, in relation to the effect of tryptophan on enhanced nucleocytoplasmic translocation of mRNA was investigated. In the standard treatment regimen, tryptophan (30 mg/100 gm of body weight) was administered by stomach tube 10 minutes before killing. The following results were noted in the liver: Administration of tryptophan increased [14C]glucosamine incorporation into proteins of the subcellular fractions, particularly those of the soluble, nucleus and nuclear membrane. In vivo treatment of rats with tryptophan increased the in vitro [14C]orotate-labeled nuclear RNA release and [3H]tryptophan binding to proteins of the nuclei or cytosols. Treatment of cytosol proteins with alpha-mannosidase or beta-galactosidase, but not with neuraminidase, inhibited these increases. After treatment of cytosol fractions on a concanavalin A agarose column, the effluents showed decreased activity and the eluates showed increased activity in in vitro nuclear RNA release and in tryptophan binding to proteins of the control and, particularly, of the tryptophan-treated animals. Administration of tryptophan increased the polyribosomal aggregation, the in vitro [14C]leucine incorporation into protein, and the in vitro nuclear RNA release by cytosol. However, tunicamycin pretreatment of rats prevented these increases due to tryptophan. The data of this study suggest that glycosylated proteins, one or more, are the active components whereby tryptophan acts upon the liver.
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PMID:Evidence for the role of glycosylation of proteins in the tryptophan-induced stimulation of nucleocytoplasmic translocation of mRNA in rat liver. 394 45

DNA from a transducing bacteriophage carrying a fusion of the tryptophan and lactose operons of E. coli (lambdadtrp-lac) has been used to direct cell-free synthesis of beta-galactosidase (EC 3.2.1.23). Whereas normal lac operon (lambdadlac) DNA requires adenosine-3':5'-cyclic monophosphate (cAMP) for beta-galactosidase synthesis, trp-lac DNA is unaffected by cAMP. This difference in cAMP dependence verifies the presence of a cAMP-requiring promoter in the lac operon that has been removed from the trp-lac DNA. Synthesis with trp-lac DNA is controlled by the protein product of the tryptophan repressor gene (trpR). Synthesis in extracts of trpR(-) (repressor-negative) cells is progressively reduced by increased additions of extract from trpR(+) cells. No trpR(-) product repression is seen when beta-galactosidase synthesis is programmed by normal lac DNA. This highly sensitive and specific assay has facilitated quantitation and partial purification of the trp repressor.
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PMID:Detection and isolation of the repressor protein for the tryptophan operon of Escherichia coli. 433 82

Fusidic acid or chloramphenicol was used to inhibit peptide synthesis to 1% of normal in Escherichia coli B, strain AS19. After 10 min of inhibition, peptide synthesis could be quickly restored to 80% of the normal rate after washing the bacteria on a filter. However, even in the presence of adenosine 3'-5'-cyclic-monophosphoric acid to block catabolite repression, beta-galactosidase, the first enzyme of the lactose operon (lac), could only be induced to 10% of normal, and the last enzyme of the operon, galactoside acetyltransferase, even less. The first and last enzymes of the operon for tryptophan synthesis could be derepressed to about 30% of normal. The lac ribonucleic acid (RNA) induced during recovery showed a smaller than normal size distribution on sucrose gradients. The operator-proximal or -distal parts of this RNA were specifically labeled. Hybridization to phi80dlac deoxyribonucleic acid (DNA) suggested that although the distal parts of the lac RNA were barely detectable, initiation was occurring at normal rates in recovery. Either normal levels of distal messenger RNA (mRNA) are made but then rapidly degraded or the mRNA is not completed. The small amount that is made decayed abnormally slowly, probably as a result of slower transcription. Total mRNA decay was multiphasic with all components decaying slower than normal. We propose that there is a residual level of inhibition of peptide synthesis during recovery. The probability that a ribosome is blocked at any codon can be estimated from the data. The longer the message, the less likely its complete translation. We propose that the RNA polymerase can transcribe translatable mRNA for only a finite distance beyond the lead ribosome. Because ribosomes can load at the start of each message in a polycistronic mRNA, the probability that a distal message will be synthesized and translated is a function of the number of more proximal messages and the distances between their ribosome-loading sites.
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PMID:Residual polarity and transcription-translation coupling during recovery from chloramphenicol or fusidic acid. 435 50

Pyridoxineless mutants of Escherichia coli B stopped incorporation of nucleosides into trichloroacetic acid-insoluble material about 40 to 60 min after pyridoxine starvation was initiated, whereas incorporation of amino acids (measured the same way) slowed but did not stop for several hours. Both these incorporations and cell density were increased most effectively by the presence of either threonine or isoleucine. Arginine, glutamate, histidine, methionine, tryptophan, and tyrosine also caused significant but less dramatic increases. Inducibility of beta-galactosidase continued beyond the point where nucleic acids appeared to stop their synthesis, suggesting that messenger ribonucleic acid synthesis continued beyond ribosomal ribonucleic acid synthesis. This inducibility was also increased by isoleucine and threonine. The overall results suggest that the threonine-isoleucine biosynthetic pathway is the most sensitive to starvation for pyridoxine.
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PMID:Isoleucine and threonine can prolong protein and ribonucleic acid synthesis in pyridoxine-starved mutants of Escherichia coli B. 456 72

Cells of Salmonella typhimurium strain SL 282, deflagellated by mechanical shear, regenerated their flagella in the absence of tryptophan, an amino acid required for growth but not found in flagellin. Ribonucleic acid (RNA) synthesis was severely inhibited by tryptophan starvation. These findings suggested that the messenger RNA (mRNA) for flagellin might be stable. Actinomycin D was used to inhibit RNA synthesis in ethylenediaminetetraacetate-treated bacteria. The introduction of an F(lac) episome into strain SL 282 permitted the simultaneous study of the synthesis of flagellin, beta-galactosidase, and total protein. In the actinomycin-treated bacteria protein and beta-galactosidase syntheses were inhibited by 90%, whereas flagellin synthesis was unaffected. We conclude that the mRNA for flagellin synthesis is stable and that species of mRNA vary with respect to metabolic stability in S. typhimurium.
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PMID:Heterogeneity of the stability of messenger ribonucleic acid in Salmonella typhimurium. 533 88

A fusion between the genes for bacteriorhodopsin and beta-galactosidase was constructed on a multicopy plasmid, pXB/Gal 101. The fusion gene, containing the bacteriorhodopsin gene fused upstream from the beta-galactosidase gene, was under the control of tandem lipoprotein and lac gene promoters. When expressed in Escherichia coli the fusion protein retained beta-galactosidase activity. Mutations in the fusion gene were produced by passage of pXB/Gal 101 through the E. coli mutator strain mut D5. Amber mutations were then selected by examining the loss of the lac+ phenotype imparted by the fusion protein to lac- E. coli cells. Amber mutations occurring within the bacteriorhodopsin gene were localized by replacing the beta-galactosidase region of each mutant plasmid with a beta-galactosidase region which was known to be unmutated. Precise localization of the mutations was achieved first by sizing the prematurely terminated peptides produced by the mutant plasmids in in vitro coupled transcription-translation reactions, and secondly by DNA sequence analysis. Six amber mutants in the gene for bacteriorhodopsin were characterized in this way. One of these was a transversion mutation at a lysine codon; the other five were all transition mutations at tryptophan codons, codons 10, 12, 80, 86, and 137 of the bacteriorhodopsin sequence.
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PMID:Introduction and characterization of amber mutations in the bacteriorhodopsin gene. 630 86

An investigation of repression in the trp system of Escherichia coli was undertaken using operon fusions and plasmids constructed via recombinant DNA technology. The promoters of the trp operon and the trpR gene were fused to lacZ, enabling the activity of these promoters to be evaluated under various conditions through measurements of beta-galactosidase production. In confirmation of earlier studies, the trpR gene was shown to be regulated autogenously. This control feature of the trp system was found to maintain intracellular Trp repressor protein at essentially invariant levels under most conditions studied. Increasing the trpR+ gene dosage did not significantly elevate Trp repressor protein levels, nor did the introduction of additional operator "sinks" result in significantly decreased levels of Trp repressor protein. Definite alterations in intracellular Trp repressor protein levels were achieved only by subverting the normal trpR regulatory elements. The placement of the lacUV5 or the lambda PL promoters upstream of the trpR gene resulted in significant increases in repression of the trp system. Substituting the primary trp promoter/operator for the native trpR promoter/operator resulted in an altered regulatory response of the trp system to tryptophan limitation or excess. The regulation of the trpR gene effectively imparts a broad range of expression to the trp operon in a manner finely attuned to fluctuations in intracellular tryptophan levels.
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PMID:Analysis in vivo of factors affecting the control of transcription initiation at promoters containing target sites for trp repressor. 631 45

We investigated whether there is translational coupling between the tryptophan operon trpB and trpA genes in Escherichia coli. A trp-lac fusion system was used in which part of the trpA gene is fused to the lacZ gene. This fusion protein has the translation initiation site of trpA but retains beta-galactosidase activity. We introduced a frameshift mutation early in trpB and measured its effect on transcription and translation of the trp-lac fusion. The mutation resulted in a 10-fold drop in beta-galactosidase activity but only a 2-fold drop in lacZ mRNA or galactoside transacetylase levels. An rho mutation restored the lacZ mRNA and transacetylase levels to those of the control but only increased the beta-galactosidase level to 20% that of the control. We conclude from these results that if the trpB gene is not translated, efficient translation of the trpA'-lac'Z mRNA does not occur and, thus, that these genes are translationally coupled. The implication of this finding for other studies with gene fusions is discussed.
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PMID:Translational coupling of the trpB and trpA genes in the Escherichia coli tryptophan operon. 631 55

Bacteriophage lambda ppheA-lac was used to obtain strains of Escherichia coli K-12 in which pheA and lacZ are each transcribed from a separate pheA promoter. Mutants in which both beta-galactosidase and chorismate mutase P-prephenate dehydratase (the pheA gene product) were derepressed were isolated, and a transacting gene (pheR) was identified. pheR was mapped at min 93 on the E. coli chromosome; pheR mutants acquired the wild-type phenotype when either F117 (which covers the 93-min region) or F116 (which covers min 59 to 65) was introduced into the cell. A rifampin resistance mutation, rpoB366, was found to derepress transcription of the pheA operon. pheR and rpoB366 affected two different systems for the phenylalanine-mediated control of pheA. A mutation in miaA (trpX), a gene known to be involved in attenuation in the tryptophan operon, was also shown to increase transcription of the pheA gene.
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PMID:Regulation of phenylalanine biosynthesis in Escherichia coli K-12: control of transcription of the pheA operon. 704 84


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