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Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The transcription program of bacteriophage T7 in vivo was analyzed by hybridizing T7 mRNAs, labeled at intervals after infection, to Hpa I restriction fragments of T7 DNA. Transcripcion of the late genes is temporally regulated: class II genes are transcribed between 4 and 16 min after infection; most class III genes are transcribed from 8 min after infection until lysis. Genes 8--10 are transcribed as both class II and class III genes. The rate of T7 RNA synthesis decreases sharply at 10 min after infection. The rapid decrease in the rate of T7 RNA synthesis and the shutoff of class II RNA synthesis were not observed in cells infected with phage defective in gene 3.5 (lysozyme). Although the decrease in the rate of T7 RNA synthesis is independent of DNA replication, the failure to shut off class II RNA synthesis normally in 3.5-- -infected cells may reflect the role of T7 lysozyme in DNA replication. In vitro, the regions of T7 DNA transcribed by the phage RNA polymerase were found to be dependent upon ionic conditions.
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PMID:Regulation of transcription of the late genes of bacteriophage T7. 27 44

Through the use of phage mutants in which various combinations of the early genes are active, and in which late gene expression is blocked, we have examined the roles of each of the five early gene products of bacteriophage T7 in regulating the synthesis of host RNA and proteins. At least two independent transcriptional controls operate during bacteriophage T7 development. The product of gene 0.7, acting alone, leads to a rapid (by 5 min) shutoff of host transcription. In the absence of gene 0.7 function, and in the absence of the phage-specified RNA polymerase, a delayed shutoff of host-dependent transcription begins at approximately 15 min after infection. This secondary control element requires either a functional gene 0.3 or gene 1.1. In the absence of any early gene products, host shutoff is not observed until much later in infection (>30 min). The delayed manner in which the products of genes 0.3 and 1.1 exert their effect suggests that their mode of action is indirect. Under conditions in which the late genes are transcribed (inefficiently) by the host RNA polymerase, gene 1.1 is observed to stimulate the synthesis of lysozyme (the product of a late phage gene). In contrast, when the late genes are transcribed by the phage-specified RNA polymerase (the product of gene 1), the kinetics of synthesis of the phage RNA polymerase itself, and of lysozyme, are not affected by the deletion of genes 0.3, 0.7, 1.1, and 1.3. We conclude that under these conditions, the products of these genes are required neither for regulation of expression of the late genes nor for the shutoff of early phage gene expression.
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PMID:Roles of the early genes of bacteriophage T7 in shutoff of host macromolecular synthesis. 33 Aug 78

A procedure is described which permits complete separation of a transcription complex formed with template DNA, growing RNA chain and functioning RNA polymerase, from RNA polymerase molecules which have bound to DNA but not initiated RNA synthesis. The method is based on the marked stability of the transcription complex to dissociation by high concentrations of CsCl or CS2SO4 which enable banding the complex after equilibrium centrifugation. With use of the newly developed procedure, affinity of Escherichia coli RNA polymerase to T7 phage DNA was found to increase during initiation of RNA synthesis but then decrease concomitant with elongation of RNA chain presumably due to migration of the enzyme to DNA sites of weak affinity. Under the conditions of maximum affinity, the transcription complex contained one core polymerase for each T7 DNA if it was isolated by centrifugation in CsCl; in contrast, 2-6 enzyme molecules remained attached on the complex when the centrifugation was carried out in Cs2SO4. Thus, RNA polymerases bound to different sites of transcription initiation appear to be distinguished based on the affinity of interaction. Attempts are also described to isolate the transcription complex in vivo by Cs2SO4 centrifugation by Brij 58-deoxycholate lysate of lysozyme-treated Escherichia coli cells. The isolated complex contained approx. 50 polymerase molecules per Escherichia coli genome as well as other unidentified proteins.
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PMID:Isolation and properties of the transcription complex of Escherichia coli RNA polymerase. 109 97

An improved method is described for the purification of the DNA-dependent RNA polymerase [ribonucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6] from Escherichia coli. The method involves lysozyme-sodium deoxycholate lysis, low-speed centrifugation, precipitation with Polymin P, elution from the Polymin P precipitate, ammonium sulfate precipitation, and chromatography on DNA-cellulose and Bio-Gel A 5m. RNA polymerase is purified to electrophoretic homogeneity in 2 days with a recovery of 45%, resulting in a yield of 250 mg of holoenzyme from 500 g of cells.
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PMID:A procedure for the rapid, large-scall purification of Escherichia coli DNA-dependent RNA polymerase involving Polymin P precipitation and DNA-cellulose chromatography. 110 52

The DNA-dependent syntheses of different enzymes of the bacteriophages T3 and T7 were studied in an Escherichia coli system in vitro with respect to the optimal Mg2+ concentration and its interdependence with substituting (e.g. spermidine) and complexing agents (e.g. phosphoenolpyruvate). The following results were obtained. 1. The optimal conditions for the syntheses of the different enzymes were not identical. The optima for RNA polymerase synthesis were 8 mM Mg2+, 10 mM P-pyruvate and 3 mM spermidine; for S-adenosyl-L-methionine cleaving enzyme synthesis, 6 mM Mg2+, 6 mM P-pyruvate and 3 mM spermidine; and for lysozyme synthesis, 13-18 mM Mg2+, 28 mM P-pyruvate and 3-0 mM spermidine. 2. The optimal conditions for the synthesis of analog enzymes (RNA polymerases and lysozymes) from the two templates were identical with experimental error. 3. Mg2+ and spermidine substituted for each other in relation to the number of their charges. 4. The apparent complexing of one Mg2+ molecule required the addition of 3-5 P pyruvate molecules. 5. Under the optimal conditions the enzyme-synthesizing activity was higher by more than a factor of 10 compared to previously described systems.
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PMID:The interdependence of magnesium with spermidine and phosphoenolpyruvate in an enzyme-synthesizing system in vitro. 126 43

The bacteriophage T7 0.7 gene encodes a protein which supports viral reproduction under specific suboptimal growth conditions. The 0.7 protein (gp0.7) shuts off host RNA polymerase-catalyzed transcription and also expresses a serine/threonine-specific, cAMP-independent protein kinase (PK) activity. To determine the role of the gp0.7 PK in viral reproduction, the 0.7 gene of the T7(JS78) mutant phage--whose gp0.7 expresses only the PK activity--was cloned in the plasmid expression vector pET-11a. Cells containing the recombinant plasmid were viable, and upon IPTG induction produced a 30-kDa polypeptide, similar in size to the gp0.7-related polypeptide seen in T7(JS78)-infected cells. Extracts of cells containing this polypeptide can phosphorylate the exogenous substrate lysozyme. Expression of plasmid-encoded gp0.7(JS78) in vivo results in phosphorylation of the same proteins which are phosphorylated in T7(JS78)-infected cells; moreover, the plasmid-encoded gp0.7(JS78) is itself phosphorylated. The JS78 mutation changes Gln243 in gp0.7 to an amber codon, which explains the production of the truncated, 30-kDa gp0.7-related polypeptide, and implicates the 11-kDa C-terminal domain in host transcription shut-off. The T7(A23) 0.7 point mutant fails to express PK activity in infected cells. However, the truncated T7(A23)-related polypeptide, expressed from a plasmid, exhibits PK activity in vivo and in vitro, but with an altered specificity. Thus, the A23 mutation, which changes Asp100 to Asn, may identify a substrate recognition determinant.
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PMID:Molecular cloning and expression of the bacteriophage T7 0.7(protein kinase) gene. 131 Jan 78

The in vivo observation that the expression of bacteriophage T7 gene 3.5 (T7 lysozyme) inactivates T7 class II transcription and the in vitro observation that T7 lysozyme inhibits T7 RNA polymerase lead to the hypothesis that T7 lysozyme might preferentially inhibit transcription from T7 class II promoters. T7 lysozyme was cloned into a lambda pL expression vector, overproduced in Escherichia coli, and purified. The ability of purified T7 lysozyme to inhibit transcription from T7 DNA, the cloned T7 class II promoters, phi 2.5 and phi 4.7, and the cloned class III promoter, phi 10, was measured in vitro. It was observed that the effectiveness of T7 lysozyme as an inhibitor of T7 RNA polymerase is inversely related to the concentration of Mg2+; T7 lysozyme inhibits T7 RNA polymerase most effectively at low Mg2+ concentrations. In addition, no preferential inhibition of transcription from cloned T7 class II promoters was observed, nor was a strong T7 class III promoter preferred when transcriptional capacity was reduced by T7 lysozyme. These observations contradict the hypotheses that the temporal control of T7 gene expression is either due to direct and selective inhibition of the T7 class II promoters by T7 lysozyme or to preferential transcription of the strong T7 class III promoters when transcriptional capacity is reduced by T7 lysozyme. It appears that alternative mechanisms such as the involvement of additional proteins and/or cellular conditions to enhance transcription from T7 class III promoters or to inhibit transcription from T7 class II promoter are necessary to explain the temporal control of transcription of bacteriophage T7.
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PMID:Inhibition of T7 RNA polymerase by T7 lysozyme in vitro. 135 74

Effects of placing a lac operator at different positions relative to a promoter for bacteriophage T7 RNA polymerase were tested. Transcription can be strongly repressed by lac repressor bound to an operator centered 15 base-pairs downstream from the RNA start, but T7 RNA polymerase initiates transcription very actively from this T7lac promoter-operator combination in the absence of repressor, or in the presence of repressor plus inducer. Sequence changes in the transcribed region were found to make transcription from some T7 promoters, including the T7lac promoter, more sensitive to inhibition by T7 lysozyme. The pET-10 and pET-11 series of plasmid vectors have been constructed to allow target genes to be placed under control of the T7lac promoter and to be expressed in BL21(DE3) or HMS174(DE3), which carry an inducible gene for T7 RNA polymerase. These vectors carry a lacI gene that provides enough lac repressor to repress both the T7lac promoter in the multicopy vectors and the chromosomal gene for T7 RNA polymerase, which is controlled by the lacUV5 promoter. Very low basal expression of target genes is achieved, but the usual high levels of expression are obtained upon induction. Addition of T7 lysozyme can reduce basal expression even further and still allow high levels of expression upon induction. Genes that are very toxic to Escherichia coli can be maintained and expressed in this system.
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PMID:Controlling basal expression in an inducible T7 expression system by blocking the target T7 promoter with lac repressor. 190 22

A number of mammalian enzymes have been expressed in Escherichia coli using the T7 RNA polymerase system, but the production of large amounts of these proteins has been limited by the low percentage of active enzyme that is found in the soluble fraction. In this report the effect of induction temperature was tested on the recovery of four rat liver enzymes, 6-phosphofructo-2-kinase/fructose-2,6- bisphosphatase, fructose-2,6-bisphosphatase, glucokinase, and fructose-1,6-bisphosphatase. We also tested the effect using a host cell strain that contains a plasmid encoding T7 lysozyme, an inhibitor of T7 RNA polymerase. Large amounts of the first three enzymes accumulated in the cells after 4 h of induction at 37 degrees C, but only about 1-2% of the total expressed proteins were recovered in a soluble, active form. When the induction was carried out at 22 degrees C for 48 h with the pLysS strain, 20- to 30-fold higher amounts of the active expressed enzymes were recovered in the soluble fraction, even though the total accumulation and the rate of synthesis of these proteins were reduced. The optimal concentration of isopropyl-1-thio-beta-D-galactopyranoside required for induction was the same at both temperatures. On the other hand, the recovery of active fructose-1,6-bisphosphatase, a heat-stable enzyme, was 66% at 37 degrees C and was essentially unchanged at an induction temperature of 22 degrees C. Lowered induction temperature would appear to be of utility for enhanced recovery of active mammalian enzymes which are insoluble in E. coli cytosol at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Expression of mammalian liver glycolytic/gluconeogenic enzymes in Escherichia coli: recovery of active enzyme is strain and temperature dependent. 196 24

Bacteriophage T7 lysozyme, a natural inhibitor of T7 RNA polymerase, can reduce basal activity from an inducible gene for T7 RNA polymerase and allow relatively toxic genes to be established in the same cell under control of a T7 promoter. Low levels of T7 lysozyme supplied by plasmids pLysS or pLysL, which are compatible with the pET vectors for expressing genes from a T7 promoter, are sufficient to stabilize many target plasmids and yet allow high levels of target protein to be produced upon induction of T7 RNA polymerase. Higher levels of lysozyme supplied by plasmids pLysE or pLysH reduce the fully induced activity of T7 RNA polymerase such that induced cells can continue to grow and produce innocuous target proteins indefinitely. Different configurations of the expression system can maintain several different steady-state levels of target gene expression. The presence of T7 lysozyme has the further advantage of facilitating the lysis of cells in preparing extracts for purification of target gene products.
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PMID:Use of bacteriophage T7 lysozyme to improve an inducible T7 expression system. 202 59


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