scholarly journals Phage genetic sites involved in lambda growth inhibition by the Escherichia coli rap mutant.

Genetics ◽  
1989 ◽  
Vol 121 (3) ◽  
pp. 401-409
Author(s):  
P Guzmán ◽  
G Guarneros
Keyword(s):  
Escherichia Coli ◽  
Growth Inhibition ◽  
Phage Genome ◽  
Bacteriophage Lambda ◽  
Phage Lambda ◽  
Wild Type ◽  
Attp Site

Abstract The rap mutation of Escherichia coli prevents the growth of bacteriophage lambda. We have isolated phage mutants that compensate for the host deficiency. The mutations, named bar, were genetically located to three different loci of the lambda genome: barI in the attP site, barII in the cIII ea10 region, and barIII within or very near the imm434 region. The level of lambda leftward transcription correlates with rap exclusion. Phage lambda mutants partially defective in the pL promoter or in pL-transcript antitermination showed a Bar- phenotype. Conversely, mutants constitutive for transcription from the pI or pL promoters were excluded more stringently by rap bacteria. We conclude that rap exclusion depends on the magnitude of transcription through the wild type bar loci in the phage genome.

Two Arabidopsis thaliana dihydrodipicolinate synthases, DHDPS1 and DHDPS2, are unequally redundant

2012 ◽  
Vol 39 (12) ◽  
pp. 1058 ◽  
Author(s):  
Susan Jones-Held ◽  
Luciana Pimenta Ambrozevicius ◽  
Michael Campbell ◽  
Bradley Drumheller ◽  
Emily Harrington ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Arabidopsis Thaliana ◽  
Growth Inhibition ◽  
Segregation Analysis ◽  
Narrow Range ◽  
Insertion Mutant ◽  
Biosynthesis Pathway ◽  
Wild Type ◽  
Exogenous Feeding ◽  
Growth Inhibitory

In Arabidopsis thalinana (L.) Heynh., DHDPS1 and DHDPS2 encode orthologous dihydrodipicolinate synthases (DHDPS), the first enzyme of the lysine (Lys) biosynthesis pathway. A TDNA insertion mutant of dhdps2 was previously reported to be viable and to accumulate free threonine (Thr). Analysis of additional TDNA insertion lines showed that dhdps1 and dhdps2 mutants are both viable and that whereas dhdps2 mutants accumulate Thr, dhdps1 plants do not. Thr-accumulation was complemented by heterologous expression of Escherichia coli DapA, indicating that the phenotype is due to reduced DHDPS activity in dhdps2. DHDPS1 contributes ~30% towards the total DHDPS activity in leaves of young plants and DHDPS2 contributes 70%; therefore, the threshold of activity resulting in Thr accumulation lies within this narrow range. dhdps1–dhdps2 double mutants could not be isolated, even after exogenous feeding with Lys. Segregation analysis indicated that gametes lacking functional DHDPS genes are defective, as are embryos. Plants carrying only a single DHDPS2 gene do not accumulate Thr, but they show a gametophytic defect that is partially rescued by Lys application. Despite the accumulation of Thr, dhdps2 seedlings are no more sensitive than wild-type plants to growth inhibition by Lys or the Lys precursor diaminopimelate. They also are not rescued by methionine at growth-inhibitory Lys concentrations. Exogenous application of Lys and methionine to dhdps2 mutants did not reduce the accumulation of Thr.

scholarly journals First-Time Isolation and Characterization of a Bacteriophage Encoding the Shiga Toxin 2c Variant, Which Is Globally Spread in Strains of Escherichia coli O157

2004 ◽  
Vol 72 (12) ◽  
pp. 7030-7039 ◽  
Author(s):  
Eckhard Strauch ◽  
Christoph Schaudinn ◽  
Lothar Beutin
Keyword(s):  
Escherichia Coli ◽  
Shiga Toxin ◽  
Phage Lambda ◽  
Wild Type ◽  
Chromosomal Locus ◽  
O157 Strain ◽  
Diagnostic Pcr ◽  
E Coli ◽  
Isolation And Characterization ◽  
K 12

ABSTRACT A bacteriophage encoding the Shiga toxin 2c variant (Stx2c) was isolated from the human Escherichia coli O157 strain CB2851 and shown to form lysogens on the E. coli K-12 laboratory strains C600 and MG1655. Production of Stx2c was found in the wild-type E. coli O157 strain and the K-12 lysogens and was inducible by growing bacteria in the presence of ciprofloxacin. Phage 2851 is the first reported viable bacteriophage which carries an stx 2c gene. Electron micrographs of phage 2851 showed particles with elongated hexagonal heads and long flexible tails resembling phage lambda. Sequence analysis of an 8.4-kb region flanking the stx 2c gene and other genetic elements revealed a mosaic gene structure, as found in other Stx phages. Phage 2851 showed lysis of E. coli K-12 strains lysogenic for Stx phages encoding Stx1 (H19), Stx2 (933W), Stx (7888), and Stx1c (6220) but showed superinfection immunity with phage lambda, presumably originating from the similarity of the cI repressor proteins of both phages. Apparently, phage 2851 integrates at a different chromosomal locus than Stx2 phage 933W and Stx1 phage H19 in E. coli, explaining why Stx2c is often found in combination with Stx1 or Stx2 in E. coli O157 strains. Diagnostic PCR was performed to determine gene sequences specific for phage 2851 in wild-type E. coli O157 strains producing Stx2c. The phage 2851 q and o genes were frequently detected in Stx2c-producing E. coli O157 strains, indicating that phages related to 2851 are associated with Stx2c production in strains of E. coli O157 that were isolated in different locations and time periods.

scholarly journals Heteroduplex chain polarity in recombination of phage lambda by the red, RecBCD, RecBC(D-) and RecF pathways.

Genetics ◽  
1991 ◽  
Vol 128 (1) ◽  
pp. 7-22 ◽  
Author(s):  
I Siddiqi ◽  
M M Stahl ◽  
F W Stahl
Keyword(s):  
Escherichia Coli ◽  
Genetic Map ◽  
Bacteriophage Lambda ◽  
The Other ◽  
Genetic Contribution ◽  
Phage Lambda ◽  
Heteroduplex Dna ◽  
Recf Pathway ◽  
The Right ◽  
Parental Information

Abstract We have examined the chain polarity of heteroduplex DNA in unreplicated, bacteriophage lambda splice recombinants when recombination was by the RecBCD, RecBC(D-), or RecF pathway of Escherichia coli or the Red pathway of lambda. For each of these pathways, recombination is activated by the cutting of cos that accompanies chromosome packaging, and is effected by recombination enzymes acting at the right end created by that cutting. For exchanges occurring near cos, one parent makes a lesser physical and genetic contribution than does the other. For each pathway, when the phage carried standard cos, this minority contribution was predominantly on the r chain, ending 5' at the right end of lambda. When standard cos was replaced by a cloned inverted cos located centrally on the standard lambda genetic map, minority contribution was predominantly on the l chain. In each case, the polarity of the overlap was usually that formed by 3' overhangs of parental information and material. These results are discussed in the context of current models of recombination for the different pathways.

scholarly journals Interaction between the sbcC gene of Escherichia coli and the gam gene of phage lambda.

Genetics ◽  
1989 ◽  
Vol 123 (2) ◽  
pp. 249-253 ◽  
Author(s):  
S K Kulkarni ◽  
F W Stahl
Keyword(s):  
Escherichia Coli ◽  
Phage Lambda ◽  
Wild Type

Abstract gam mutants of phage lambda carrying long palindromes fail to form plaques on wild-type Escherichia coli but do grow on strains that are mutant in the sbcC gene. gam + lambda carrying the same palindrome grow on both hosts and on a host deleted for the recB, C and D genes. These results suggest that the Gam protein of lambda, known to interact also with E. coli's recBCD protein, can interact with the product of the sbcC gene.

scholarly journals Saturation of DNA Mismatch Repair and Error Catastrophe by a Base Analogue in Escherichia coli

Genetics ◽  
2002 ◽  
Vol 161 (4) ◽  
pp. 1363-1371
Author(s):  
Kazuo Negishi ◽  
David Loakes ◽  
Roel M Schaaper
Keyword(s):  
Escherichia Coli ◽  
Mismatch Repair ◽  
Dna Mismatch Repair ◽  
Repair System ◽  
Mutagenic Action ◽  
Wild Type ◽  
Dna Mismatch ◽  
Cell Counts ◽  
Error Catastrophe ◽  
Mismatch Repair System

Abstract Deoxyribosyl-dihydropyrimido[4,5-c][1,2]oxazin-7-one (dP) is a potent mutagenic deoxycytidine-derived base analogue capable of pairing with both A and G, thereby causing G · C → A · T and A · T → G · C transition mutations. We have found that the Escherichia coli DNA mismatch-repair system can protect cells against this mutagenic action. At a low dose, dP is much more mutagenic in mismatch-repair-defective mutH, mutL, and mutS strains than in a wild-type strain. At higher doses, the difference between the wild-type and the mutator strains becomes small, indicative of saturation of mismatch repair. Introduction of a plasmid containing the E. coli mutL+ gene significantly reduces dP-induced mutagenesis. Together, the results indicate that the mismatch-repair system can remove dP-induced replication errors, but that its capacity to remove dP-containing mismatches can readily be saturated. When cells are cultured at high dP concentration, mutant frequencies reach exceptionally high levels and viable cell counts are reduced. The observations are consistent with a hypothesis in which dP-induced cell killing and growth impairment result from excess mutations (error catastrophe), as previously observed spontaneously in proofreading-deficient mutD (dnaQ) strains.

scholarly journals Semi-Synthesis of Small Molecules of Aminocarbazoles: Tumor Growth Inhibition and Potential Impact on p53

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1637
Author(s):  
Solida Long ◽  
Joana B. Loureiro ◽  
Carla Carvalho ◽  
Luís Gales ◽  
Lucília Saraiva ◽  
...  
Keyword(s):  
Growth Inhibition ◽  
Small Molecules ◽  
Tumor Cells ◽  
Mutant P53 ◽  
Wild Type ◽  
Naturally Occurring ◽  
Growth Inhibitory ◽  
Growth Inhibitory Activity ◽  
Amino Derivatives ◽  
Carbazole Alkaloids

The tumor suppressor p53 is inactivated by mutation in approximately 50% of human cancers. Small molecules that bind and stabilize those mutants may represent effective anticancer drugs. Herein, we report the tumor cell growth inhibitory activity of carbazole alkaloids and amino derivatives, as well as their potential activation of p53. Twelve aminocarbazole alkaloids were semi-synthesized from heptaphylline (1), 7-methoxy heptaphylline (2), and 7-methoxymukonal (3), isolated from Clausena harmandiana, using a reductive amination protocol. Naturally-occurring carbazoles 1–3 and their amino derivatives were evaluated for their potential effect on wild-type and mutant p53 activity using a yeast screening assay and on human tumor cell lines. Naturally-occurring carbazoles 1–3 showed the most potent growth inhibitory effects on wild-type p53-expressing cells, being heptaphylline (1) the most promising in all the investigated cell lines. However, compound 1 also showed growth inhibition against non-tumor cells. Conversely, semi-synthetic aminocarbazole 1d showed an interesting growth inhibitory activity in tumor cells expressing both wild-type and mutant p53, exhibiting low growth inhibition on non-tumor cells. The yeast assay showed a potential reactivation of mutant p53 by heptaphylline derivatives, including compound 1d. The results obtained indicate that carbazole alkaloids may represent a promising starting point to search for new mutp53-reactivating agents with promising applications in cancer therapy.

scholarly journals Escherichia coli MutM Suppresses Illegitimate Recombination Induced by Oxidative Stress

Genetics ◽  
1999 ◽  
Vol 151 (2) ◽  
pp. 439-446 ◽  
Author(s):  
Masaaki Onda ◽  
Katsuhiro Hanada ◽  
Hirokazu Kawachi ◽  
Hideo Ikeda
Keyword(s):  
Oxidative Stress ◽  
Escherichia Coli ◽  
Hydrogen Peroxide ◽  
Dna Damage ◽  
Double Strand Breaks ◽  
Illegitimate Recombination ◽  
Recombination Analysis ◽  
Wild Type ◽  
Strand Breaks ◽  
In The Wild

Abstract DNA damage by oxidative stress is one of the causes of mutagenesis. However, whether or not DNA damage induces illegitimate recombination has not been determined. To study the effect of oxidative stress on illegitimate recombination, we examined the frequency of λbio transducing phage in the presence of hydrogen peroxide and found that this reagent enhances illegitimate recombination. To clarify the types of illegitimate recombination, we examined the effect of mutations in mutM and related genes on the process. The frequency of λbio transducing phage was 5- to 12-fold higher in the mutM mutant than in the wild type, while the frequency in the mutY and mutT mutants was comparable to that of the wild type. Because 7,8-dihydro-8-oxoguanine (8-oxoG) and formamido pyrimidine (Fapy) lesions can be removed from DNA by MutM protein, these lesions are thought to induce illegitimate recombination. Analysis of recombination junctions showed that the recombination at Hotspot I accounts for 22 or 4% of total λbio transducing phages in the wild type or in the mutM mutant, respectively. The preferential increase of recombination at nonhotspot sites with hydrogen peroxide in the mutM mutant was discussed on the basis of a new model, in which 8-oxoG and/or Fapy residues may introduce double-strand breaks into DNA.

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