scholarly journals Radiation-Induced Reversion of Transition Mutants

1964 ◽  
Vol 17 (4) ◽  
pp. 907 ◽  
Author(s):  
GW Grigg
Keyword(s):  
Escherichia Coli ◽  
Protein Synthesis ◽  
Base Pair ◽  
The Other ◽  
Wild Type ◽  
Lethal Effects ◽  
Reversion Frequency ◽  
X Irradiation ◽  
Radiation Induced ◽  
Adenine Thymine

X-irradiation increased the reversion frequency of two transition mutants of Escherichia coli, one of which (meth-) differed genetically from wild type by an adenine-thymine substitution of a guanine-cytosine base pair, the other (urg-2-) by a guanine-cytosine substitution of an adenine-thymine base pair. The lethal effects of the radiation were greatest when protein synthesis was prevented for a period immediately after irradiation. A period of 30 min at 37�0 was as effective as 22 hr. Irradiation of a saline suspension gave a lower survival of 0�2 times that of bacteria irradiated after being spread on minimal agar plates.

scholarly journals Lethal Action of Quinolones against a Temperature-Sensitive dnaB Replication Mutant of Escherichia coli

2006 ◽  
Vol 50 (1) ◽  
pp. 362-364 ◽  
Author(s):  
Xilin Zhao ◽  
Muhammad Malik ◽  
Nymph Chan ◽  
Alex Drlica-Wagner ◽  
Jian-Ying Wang ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Protein Synthesis ◽  
Dna Replication ◽  
Nalidixic Acid ◽  
Temperature Sensitive ◽  
Wild Type ◽  
Lethal Action ◽  
Inhibition Of Protein Synthesis

ABSTRACT Inhibition of DNA replication in an Escherichia coli dnaB-22 mutant failed to block quinolone-mediated lethality. Inhibition of protein synthesis by chloramphenicol inhibited nalidixic acid lethality and, to a lesser extent, ciprofloxacin lethality in both dnaB-22 and wild-type cells. Thus, major features of quinolone-mediated lethality do not depend on ongoing replication.

Homologous recombination involving a large heterology in Escherichia coli.

Genetics ◽  
1988 ◽  
Vol 119 (4) ◽  
pp. 759-769
Author(s):  
K Yamamoto ◽  
N Takahashi ◽  
H Yoshikura ◽  
I Kobayashi
Keyword(s):  
Escherichia Coli ◽  
Gene Conversion ◽  
Kanamycin Resistance ◽  
Coli Strain ◽  
The Other ◽  
Reca Gene ◽  
Inverted Repeats ◽  
Crossing Over ◽  
Wild Type ◽  
Parental Allele

Abstract Recombination between two different deletion alleles of a gene (neo) for neomycin and kanamycin resistance was studied in an Escherichia coli sbcA- recB-C- strain. The two homologous regions were in an inverted orientation on the same plasmid molecule. Kanamycin-resistant plasmids were selected and analyzed. The rate of recombination to form kanamycin-resistant plasmids was decreased by mutations in the recE, recF and recJ genes, but was not decreased by a mutation in the recA gene. It was found that these plasmids often possessed one wild-type kanamycin-resistant allele (neo+) while the other neo allele was still in its original (deletion) form. Among kanamycin-resistant plasmids with one wild-type and one parental allele it was often found that the region between the inverted repeats had been flipped (turned around) with respect to sites outside the inverted repeats. These results were interpreted as follows. Gene conversion, analogous to gene conversion in eukaryotic meiosis, is responsible for a unidirectional transfer of information from one neo deletion allele to the other. The flipping of the region between the inverted repeats is interpreted as analogous to the crossing over associated with gene conversion in eukaryotic meiosis. In contrast with a rec+ strain, these products cannot be explained by two rounds of reciprocal crossing over involving a dimeric form as an intermediate. In the accompanying paper we present evidence that gene conversion by double-strand gap repair takes place in the same E. coli strain.

scholarly journals Differential Biological and Adjuvant Activities of Cholera Toxin and Escherichia coli Heat-Labile Enterotoxin Hybrids

2001 ◽  
Vol 69 (3) ◽  
pp. 1528-1535 ◽  
Author(s):  
Christal C. Bowman ◽  
John D. Clements
Keyword(s):  
Escherichia Coli ◽  
Cyclic Amp ◽  
Cholera Toxin ◽  
The Other ◽  
Toxin Gene ◽  
Wild Type ◽  
B Subunit ◽  
Heat Labile ◽  
A Subunit ◽  
Ifn Γ

ABSTRACT Two bacterial products that have been demonstrated to function as mucosal adjuvants are cholera toxin (CT), produced by various strains of Vibrio cholerae, and the heat-labile enterotoxin (LT) produced by some enterotoxigenic strains of Escherichia coli. Although LT and CT have many features in common, they are clearly distinct molecules with biochemical and immunologic differences which make them unique. The goal of this study was to determine the basis for these biological differences by constructing and characterizing chimeric CT-LT molecules. Toxin gene fragments were subcloned to create two constructs, each expressing the enzymatically active A subunit of one toxin and the receptor binding B subunit of the other toxin. These hybrid toxins were purified, and the composition and assembly of CT A subunit (CT-A)-LT B subunit (LT-B) and LT A subunit (LT-A)-CT B subunit (CT-B) were confirmed. Hybrids were evaluated for enzymatic activity, as measured by the accumulation of cyclic AMP in Caco-2 cells, and the enterotoxicity of each toxin was assessed in a patent-mouse assay. The results demonstrated that LT-A–CT-B induces the accumulation of lower levels of cyclic AMP and has less enterotoxicity than either wild-type toxin or the other hybrid. Nonetheless, this hybrid retains adjuvant activity equivalent to or greater than that of either wild-type toxin or the other hybrid when used in conjunction with tetanus toxoid for intranasal immunization of BALB/c mice. Importantly, the ability of LT to induce a type 1 cytokine response was found to be a function of LT-A. Specifically, LT-A–CT-B was able to augment the levels of antigen-specific gamma interferon (IFN-γ) and interleukin 5 to levels comparable to those achieved with native LT, while CT-A–LT-B and native CT both produced lower levels of antigen-specific IFN-γ. Thus, these toxin hybrids possess unique biological characteristics and provide information about the basis for differences in the biological activities observed for CT and LT.

scholarly journals Effects of oxygen on aerosol survival of radiation sensitive and resistant strains ofEscherichia coliB

1971 ◽  
Vol 69 (4) ◽  
pp. 661-672 ◽  
Author(s):  
C. S. Cox ◽  
M. C. Bondurant ◽  
M. T. Hatch
Keyword(s):  
Escherichia Coli ◽  
Relative Humidity ◽  
Metabolic Activity ◽  
Radiation Sensitivity ◽  
The Other ◽  
E Coli ◽  
Radiation Induced ◽  
Resistant Strains ◽  
Resistant Mutants ◽  
Survival In Air

SUMMARYThe aerosol survivals in air and nitrogen of radiation sensitive and resistant mutants ofEscherichia coliB have been determined with logarithmic and resting phase bacteria. No consistent correlation was found between radiation sensitivity and aerosol sensitivity in the strains tested. Hence, the phenotypes Fil Her Exr, which determine sensitivity to radiation, do not influence aerosol survival, i.e. these known mechanisms which repair radiation-induced damage do not operate in aerosol stressedE. coli. In all cases the survival in air was less than that in nitrogen particularly so forE. coliBs-1. The effect is explained in terms of a toxic action of oxygen. Comparison of survival of log and resting phase bacteria show that log phase cells are less aerosol stable than are resting phase cells. The ability to synthesize DNA in bacteria collected from the aerosol was less than in control unstressed bacteria, and this effect was independent of the presence of oxygen. Reduced ability to synthesize DNA could have been caused by reduced metabolic activity. It is shown that two different death mechanisms occur simultaneously in aerosols at low relative humidity. One mechanism is oxygen dependent and the other oxygen independent. The former was not through a decrease in metabolic activity, whereas the latter could be.

scholarly journals Competition between trichodermin and several other sesquiterpene antibiotics for binding to their receptor site(s) on eukaryotic ribosomes

1976 ◽  
Vol 160 (2) ◽  
pp. 137-145 ◽  
Author(s):  
M Cannon ◽  
A Jimenez ◽  
D Vazquez
Keyword(s):  
Protein Synthesis ◽  
Dissociation Constant ◽  
Relative Efficiency ◽  
Type Strain ◽  
Wild Type Strain ◽  
Receptor Site ◽  
The Other ◽  
Wild Type ◽  
Inhibit Protein Synthesis ◽  
Run Off

1. Of the five sesquiterpene antibiotics tested and found to inhibit protein synthesis in yeast spheroplasts, trichothecin, trichodermol or trichodermin stabilized polyribosomes whereas, in contrast, verrucarin A or T-2 toxin induced ‘run off’ of polyribosomes with a corresponding increase in 80S monoribosomes. The effect of fusarenon X on the system could not be determined as the drug failed to enter the cells. 2. [acetyl-14C]Trichodermin bound to yeast polyribosomes with a dissociation constant of 2.10 muM and to yeast ‘run off’ ribosomes with a dissociation constant of 0.72 muM. 3. Trichothecin, trichodermol, fusarenon X, T-2 toxin and verrucarin A competed with [acetyl-14C]trichodermin for binding to its receptor site on ‘run off’ ribosomes. The observed competition was quantitatively similar for all drugs tested. In contrast, the five drugs competed to different extents with trichodermin for binding to its receptor site on polyribosomes. Thus trichothecin competed with relative efficiency, whereas verrucarin A competed poorly, and the other drugs occupied intermediate positions between these two extremes. 4. Studies were also carried out with yeast ‘run off’ ribosomes prepared from both a wild-type strain and a strain resistant to trichodermin. Competition experiments between verrucarin A and [3H]anisomycin indicated that verrucarin A bound to ‘run off’ ribosomes from the mutant strain less efficiently than to those from the wild-type.

scholarly journals Genetic Analysis of the Invariant Residue G791 in Escherichia coli 16S rRNA Implicates RelA in Ribosome Function

2009 ◽  
Vol 191 (7) ◽  
pp. 2042-2050 ◽  
Author(s):  
Hong-Man Kim ◽  
Sang-Mi Ryou ◽  
Woo-Seok Song ◽  
Se-Hoon Sim ◽  
Chang-Jun Cha ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Protein Synthesis ◽  
16S Rrna ◽  
Stringent Response ◽  
State Level ◽  
Synthetic Activity ◽  
Wild Type ◽  
Multicopy Suppressor ◽  
Invariant Residue ◽  
In Cells

ABSTRACT Previous studies identified G791 in Escherichia coli 16S rRNA as an invariant residue for ribosome function. In order to establish the functional role of this residue in protein synthesis, we searched for multicopy suppressors of the mutant ribosomes that bear a G-to-U substitution at position 791. We identified relA, a gene whose product has been known to interact with ribosomes and trigger a stringent response. Overexpression of RelA resulted in the synthesis of approximately 1.5 times more chloramphenicol acetyltransferase (CAT) protein than could be synthesized by the mutant ribosomes in the absence of RelA overexpression. The ratio of mutant rRNA to the total ribosome pool was not changed, and the steady-state level of CAT mRNA was decreased by RelA overexpression. These data confirmed that the phenotype of RelA as a multicopy suppressor of the mutant ribosome did not result from the enhanced synthesis of mutant rRNA or CAT mRNA from the plasmid. To test whether the phenotype of RelA was related to the stringent response induced by the increased cellular level of (p)ppGpp, we screened for mutant RelA proteins whose overexpression enhances CAT protein synthesis by the mutant ribosomes as effectively as wild-type RelA overexpression and then screened for those whose overexpression does not produce sufficiently high levels of (p)ppGpp to trigger the stringent response under the condition of amino acid starvation. Overexpression of the isolated mutant RelA proteins resulted in the accumulation of (p)ppGpp in cells, which was amounted to approximately 18.2 to 38.9% of the level of (p)ppGpp found in cells that overexpress the wild-type RelA. These findings suggest that the function of RelA as a multicopy suppressor of the mutant ribosome does not result from its (p)ppGpp synthetic activity. We conclude that RelA has a previously unrecognized role in ribosome function.

scholarly journals Independent Regulation of Two Genes in Escherichia coli by Tetracyclines and Tet Repressor Variants

2004 ◽  
Vol 186 (13) ◽  
pp. 4399-4401 ◽  
Author(s):  
Annette Kamionka ◽  
Miriam Sehnal ◽  
Oliver Scholz ◽  
Wolfgang Hillen
Keyword(s):  
Escherichia Coli ◽  
Cross Talk ◽  
Reporter Genes ◽  
The Other ◽  
Regulation System ◽  
The Novel ◽  
Wild Type ◽  
Tet Repressor

ABSTRACT We report a regulation system in Escherichia coli for independent regulation of two distinct reporter genes by application of Tet repressors with different specificities. One Tet repressor variant comprises wild-type tet operator (tetO) recognition and exclusive induction with the novel inducer 4-dedimethylamino-anhydrotetracycline. The other Tet repressor variant shows tetO-4C recognition and induction with tetracycline. We demonstrate that both variants are independently active in vivo and allow selective regulation of two genes in the same cell without any cross talk.

scholarly journals Protein Synthesis in Escherichia coli with Mischarged tRNA

2003 ◽  
Vol 185 (12) ◽  
pp. 3524-3526 ◽  
Author(s):  
Bokkee Min ◽  
Makoto Kitabatake ◽  
Carla Polycarpo ◽  
Joanne Pelaschier ◽  
Gregory Raczniak ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Protein Synthesis ◽  
Elongation Factor ◽  
Trna Synthetase ◽  
Wild Type ◽  
Wild Type Level ◽  
E Coli ◽  
Missense Mutant ◽  
Tryptophan Synthetase

ABSTRACT Two types of aspartyl-tRNA synthetase exist: the discriminating enzyme (D-AspRS) forms only Asp-tRNAAsp, while the nondiscriminating one (ND-AspRS) also synthesizes Asp-tRNAAsn, a required intermediate in protein synthesis in many organisms (but not in Escherichia coli). On the basis of the E. coli trpA34 missense mutant transformed with heterologous ND-aspS genes, we developed a system with which to measure the in vivo formation of Asp-tRNAAsn and its acceptance by elongation factor EF-Tu. While large amounts of Asp-tRNAAsn are detrimental to E. coli, smaller amounts support protein synthesis and allow the formation of up to 38% of the wild-type level of missense-suppressed tryptophan synthetase.

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