scholarly journals Mechanisms of Dinucleotide Repeat Instability in Escherichia coli

Genetics ◽  
2000 ◽  
Vol 154 (2) ◽  
pp. 533-542
Author(s):  
Marc Bichara ◽  
Isabelle Pinet ◽  
Sylvie Schumacher ◽  
Robert P P Fuchs
Keyword(s):  
Escherichia Coli ◽  
Mismatch Repair ◽  
Genetic Instability ◽  
Positional Cloning ◽  
Dinucleotide Repeats ◽  
Disease Pathogenesis ◽  
Complementary Sequence ◽  
Phylogenetic Studies ◽  
High Level

Abstract The high level of polymorphism of microsatellites has been used for a variety of purposes such as positional cloning of genes associated with diseases, forensic medicine, and phylogenetic studies. The discovery that microsatellites are associated with human diseases, not only as markers of risk but also directly in disease pathogenesis, has triggered a renewed interest in understanding the mechanism of their instability. In this work we have investigated the role of DNA replication, long patch mismatch repair, and transcription on the genetic instability of all possible combinations of dinucleotide repeats in Escherichia coli. We show that the (GpC) and (ApT) self-complementary sequence repeats are the most unstable and that the mode of replication plays an important role in their instability. We also found that long patch mismatch repair is involved in avoiding both short deletion and expansion events and also in instabilities resulting from the processing of bulges of 6 to 8 bp for the (GpT/ApC)- and (ApG/CpT)-containing repeats. For each dinucleotide sequence repeat, we propose models for instability that involve the possible participation of unusual secondary structures.

scholarly journals Molecular survey of mcr1 and mcr2 plasmid mediated colistin resistance genes in Escherichia coli isolates of animal origin in Iran

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Kayhan Ilbeigi ◽  
Mahdi Askari Badouei ◽  
Hossein Vaezi ◽  
Hassan Zaheri ◽  
Sina Aghasharif ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Resistance Genes ◽  
Companion Animals ◽  
Multidrug Resistant ◽  
Animal Origin ◽  
Colistin Resistance ◽  
E Coli ◽  
High Level ◽  
Farming Industry

Abstract Objectives The emergence of colistin-resistant Enterobacteriaceae from human and animal sources is one of the major public health concerns as colistin is the last-resort antibiotic for treating infections caused by multidrug-resistant Gram-negative bacteria. We aimed to determine the prevalence of the prototype widespread colistin resistance genes (mcr-1 and mcr-2) among commensal and pathogenic Escherichia coli strains isolated from food-producing and companion animals in Iran. Results A total of 607 E. coli isolates which were previously collected from different animal sources between 2008 and 2016 used to uncover the possible presence of plasmid-mediated colistin resistance genes (mcr-1 and mcr-2) by PCR. Overall, our results could not confirm the presence of any mcr-1 or mcr-2 positive E. coli among the studied isolates. It is concluded that despite the important role of food-producing animals in transferring the antibiotic resistance, they were not the main source for carriage of mcr-1 and mcr-2 in Iran until 2016. This study suggests that the other mcr variants (mcr-3 to mcr-9) might be responsible for conferring colistin resistance in animal isolates in Iran. The possible linkage between pig farming industry and high level of mcr carriage in some countries needs to be clarified in future prospective studies.

scholarly journals Longitudinal Study of Escherichia coli O157:H7 in a Beef Cattle Feedlot and Role of High-Level Shedders in Hide Contamination

2009 ◽  
Vol 75 (20) ◽  
pp. 6515-6523 ◽  
Author(s):  
Terrance M. Arthur ◽  
James E. Keen ◽  
Joseph M. Bosilevac ◽  
Dayna M. Brichta-Harhay ◽  
Norasak Kalchayanand ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Longitudinal Study ◽  
Beef Cattle ◽  
Intervention Studies ◽  
High Density ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
High Level ◽  
Cattle Feedlot

ABSTRACT The objectives of the study described here were (i) to investigate the dynamics of Escherichia coli O157:H7 fecal and hide prevalence over a 9-month period in a feedlot setting and (ii) to determine how animals shedding E. coli O157:H7 at high levels affect the prevalence and levels of E. coli O157:H7 on the hides of other animals in the same pen. Cattle (n = 319) were distributed in 10 adjacent pens, and fecal and hide levels of E. coli O157:H7 were monitored. When the fecal pen prevalence exceeded 20%, the hide pen prevalence was usually (25 of 27 pens) greater than 80%. Sixteen of 19 (84.2%) supershedder (>104 CFU/g) pens had a fecal prevalence greater than 20%. Significant associations with hide and high-level hide (≥40 CFU/100 cm2) contamination were identified for (i) a fecal prevalence greater than 20%, (ii) the presence of one or more high-density shedders (≥200 CFU/g) in a pen, and (iii) the presence of one or more supershedders in a pen. The results presented here suggest that the E. coli O157:H7 fecal prevalence should be reduced below 20% and the levels of shedding should be kept below 200 CFU/g to minimize the contamination of cattle hides. Also, large and unpredictable fluctuations within and between pens in both fecal and hide prevalence of E. coli O157:H7 were detected and should be used as a guide when preharvest studies, particularly preharvest intervention studies, are designed.

scholarly journals The Oxidized Deoxynucleoside Triphosphate Pool Is a Significant Contributor to Genetic Instability in Mismatch Repair-Deficient Cells

2004 ◽  
Vol 24 (1) ◽  
pp. 465-474 ◽  
Author(s):  
Maria Teresa Russo ◽  
Monica Francesca Blasi ◽  
Federica Chiera ◽  
Paola Fortini ◽  
Paolo Degan ◽  
...  
Keyword(s):  
Mismatch Repair ◽  
Mutation Rate ◽  
Genetic Instability ◽  
Mammalian Cells ◽  
Spontaneous Mutation ◽  
Cancer Cell Line ◽  
Spontaneous Mutation Rate ◽  
Mutator Phenotype ◽  
Dntp Pool ◽  
High Level

ABSTRACT Oxidation is a common form of DNA damage to which purines are particularly susceptible. We previously reported that oxidized dGTP is potentially an important source of DNA 8-oxodGMP in mammalian cells and that the incorporated lesions are removed by DNA mismatch repair (MMR). MMR deficiency is associated with a mutator phenotype and widespread microsatellite instability (MSI). Here, we identify oxidized deoxynucleoside triphosphates (dNTPs) as an important cofactor in this genetic instability. The high spontaneous hprt mutation rate of MMR-defective msh2 −/− mouse embryonic fibroblasts was attenuated by expression of the hMTH1 protein, which degrades oxidized purine dNTPs. A high level of hMTH1 abolished their mutator phenotype and restored the hprt mutation rate to normal. Molecular analysis of hprt mutants showed that the presence of hMTH1 reduced the incidence of mutations in all classes, including frameshifts, and also implicated incorporated 2-oxodAMP in the mutator phenotype. In hMSH6-deficient DLD-1 human colorectal carcinoma cells, overexpression of hMTH1 markedly attenuated the spontaneous mutation rate and reduced MSI. It also reduced the incidence of −G and −A frameshifts in the hMLH1-defective DU145 human prostatic cancer cell line. Our findings indicate that incorporation of oxidized purines from the dNTP pool may contribute significantly to the extreme genetic instability of MMR-defective human tumors.

scholarly journals Role of the Cold-Box Region in the 5′ Untranslated Region of the cspA mRNA in Its Transient Expression at Low Temperature in Escherichia coli

1998 ◽  
Vol 180 (1) ◽  
pp. 90-95 ◽  
Author(s):  
Li Fang ◽  
Yan Hou ◽  
Masayori Inouye
Keyword(s):  
Escherichia Coli ◽  
Low Temperature ◽  
Untranslated Region ◽  
Cold Shock ◽  
Wild Type ◽  
Mrna Stabilization ◽  
High Level ◽  
Cold Box ◽  
In Cells

ABSTRACT Upon temperature downshift, a group of proteins called cold shock proteins, such as CspA, CspB, and CsdA, are transiently induced inEscherichia coli. However, when the 5′ untranslated region (5′ UTR) of cspA mRNA is overproduced at low temperature, the expression of cold shock genes is prolonged or derepressed. It has been proposed that this effect is due to highly conserved 11-base sequences designated the “cold box” existing in the 5′ UTRs ofcspA, cspB, and csdA. Here, we demonstrate that the overproduction of the 5′ UTR of not onlycspA but also cspB and csdA mRNAs causes derepression of all three genes at the same time. Conversely, when the cold-box region was deleted from the cspA 5′ UTR its derepression function was abolished. The amount of mRNA from the chromosomal cspA gene was much higher in cells overproducing the wild-type 5′ UTR by means of a plasmid than it was in cells overproducing the cold-box-deleted 5′ UTR. The stability of the chromosomal cspA mRNA in cells overproducing the wild-type 5′ UTR was almost identical to that in cells overproducing the cold-box-deleted 5′ UTR. Therefore, the derepression ofcspA caused by overproduction of 5′ UTR at the end of the acclimation phase occurs at the level of transcription but not by mRNA stabilization, indicating that the cold-box region plays a negative role in cspA transcription in cold shock-adapted cells. The role of the cold-box region was further confirmed with acspA mutant strain containing a cold-box-deletedcspA gene integrated into the chromosome, which showed a high level of constitutive production of CspA but not CspB during exponential growth at low temperature.

Role of the 5´ → 3´ exonuclease and Klenow fragment of Escherichia coli DNA polymerase I in base mismatch repair

2007 ◽  
Vol 278 (2) ◽  
pp. 211-220 ◽  
Author(s):  
Masaru Imai ◽  
Yu-ichiro Tago ◽  
Makoto Ihara ◽  
Masakado Kawata ◽  
Kazuo Yamamoto
Keyword(s):  
Escherichia Coli ◽  
Mismatch Repair ◽  
Dna Polymerase ◽  
Klenow Fragment ◽  
Dna Polymerase I ◽  
Base Mismatch ◽  
Polymerase I

scholarly journals Role of the dinB Gene Product in Spontaneous Mutation in Escherichia coli with an Impaired Replicative Polymerase

2000 ◽  
Vol 182 (23) ◽  
pp. 6742-6750 ◽  
Author(s):  
B. S. Strauss ◽  
R. Roberts ◽  
L. Francis ◽  
P. Pouryazdanparast
Keyword(s):  
Escherichia Coli ◽  
Mismatch Repair ◽  
Spontaneous Mutation ◽  
Luria Bertani ◽  
Base Substitution ◽  
Temperature Sensitive ◽  
Selection Scheme ◽  
Mutator Effect ◽  
Substitution Mutations

ABSTRACT We isolated several new mutator mutations of the Escherichia coli replicative polymerase dnaE subunit alpha and used them and a previously reported dnaE mutation to study spontaneous frameshift and base substitution mutations. Two of thesednaE strains produce many more mutants when grown on rich (Luria-Bertani) than on minimal medium. A differential effect of the medium was not observed when these dnaE mutations were combined with a mismatch repair mutation. The selection scheme for thednaE mutations required that they be able to complement a temperature-sensitive strain. However, the ability to complement is not related to the mutator effect for at least one of the mutants. Comparison of the mutation rates for frameshift and base substitution mutations in mutS and dnaE mutS strains suggests that the mismatch repair proteins respond differently to the two types of change. Deletion of dinB from both chromosome and plasmid resulted in a four- to fivefold decrease in the rate of frameshift and base substitution mutations in a dnaE mutSdouble mutant background. This reduction indicates that most mistakes in replication occur as a result of the action of the auxiliary rather than the replicative polymerase in this dnaE mutant. Deletion of dinB from strains carrying a wild-typednaE had a measurable effect, suggesting that a fraction of spontaneous mutations occur as a result of dinB polymerase action even in cells with a normal replicative polymerase.

scholarly journals Role of RcsF in Signaling to the Rcs Phosphorelay Pathway in Escherichia coli

2005 ◽  
Vol 187 (19) ◽  
pp. 6770-6778 ◽  
Author(s):  
Nadim Majdalani ◽  
Michael Heck ◽  
Valerie Stout ◽  
Susan Gottesman
Keyword(s):  
Escherichia Coli ◽  
Cell Surface ◽  
Small Rna ◽  
Kinase Activity ◽  
Response Regulator ◽  
Constitutive Expression ◽  
Activation Mechanism ◽  
Sensor Kinase ◽  
High Level

ABSTRACT The rcs phosphorelay pathway components were originally identified as regulators of capsule synthesis. In addition to the transmembrane sensor kinase RcsC, the RcsA coregulator, and the response regulator RcsB, two new components have been characterized, RcsD and RcsF. RcsD, the product of the yojN gene, now renamed rcsD, acts as a phosphorelay between RcsC and RcsB. Transcription of genes for capsule synthesis (cps) requires both RcsA and RcsB; transcription of other promoters, including that for the small RNA RprA, requires only RcsB. RcsF was described as an alternative sensor kinase for RcsB. We have examined the role of RcsF in the activation of both the rprA and cps promoters. We find that a number of signals that lead to activation of the phosphorelay require both RcsF and RcsC; epistasis experiments place RcsF upstream of RcsC. The RcsF sequence is characteristic of lipoproteins, consistent with a role in sensing cell surface perturbation and transmitting this signal to RcsC. Activation of RcsF does not require increased transcription of the gene, suggesting that modification of the RcsF protein may act as an activating signal. Signals from RcsC require RcsD to activate RcsB. Sequencing of an rcsC allele, rcsC137, that leads to high-level constitutive expression of both cps and rprA suggests that the response regulator domain of RcsC plays a role in negatively regulating the kinase activity of RcsC. The phosphorelay and the variation in the activation mechanism (dependent upon or independent of RcsA) provide multiple steps for modulating the output from this system.

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