Search results for "MUTATION"
showing 10 items of 2830 documents
EGFP Reporters for Direct and Sensitive Detection of Mutagenic Bypass of DNA Lesions
2020
The sustainment of replication and transcription of damaged DNA is essential for cell survival under genotoxic stress
Cell proliferation and DNA breaks are involved in ultraviolet light-induced apoptosis in nucleotide excision repair-deficient Chinese hamster cells.
2002
UV light targets both membrane receptors and nuclear DNA, thus evoking signals triggering apoptosis. Although receptor-mediated apoptosis has been extensively investigated, the role of DNA damage in apoptosis is less clear. To analyze the importance of DNA damage induced by UV-C light in apoptosis, we compared nucleotide excision repair (NER)-deficient Chinese hamster ovary cells (lines 27-1 and 43-3B mutated for the repair genes ERCC3 and ERCC1, respectively) with the corresponding DNA repair-proficient fibroblasts (CHO-9 and ERCC1 complemented 43-3B cells). NER-deficient cells were hypersensitive as to the induction of apoptosis, indicating that apoptosis induced by UV-C light is due to u…
Mechanisms and consequences of methylating agent-induced SCEs and chromosomal aberrations: a long road traveled and still a far way to go.
2003
Since the milestone work of Evans and Scott, demonstrating the replication dependence of alkylation-induced aberrations, and Obe and Natarajan, pointing to the critical role of DNA double-strand breaks (DSBs) as the ultimate trigger of aberrations, the field has grown extensively. A notable example is the identification of DNA methylation lesions provoking chromosome breakage (clastogenic) effects, which made it possible to model clastogenic pathways evoked by genotoxins. Experiments with repair-deficient mutants and transgenic cell lines revealed both O<sup>6</sup>-methylguanine (O<sup>6</sup>MeG) and N- methylpurines as critical lesions. For S<sub>N</sub&g…
The high rate of endoreduplication in the repair deficient CHO mutant EM9 parallels a reduced level of methylated deoxycytidine in DNA
2008
It has been recently proposed that hypomethylation of DNA induced by 5-azacytidine (5-azaC) leads to reduced chromatid decatenation that ends up in endoreduplication, most likely due to a failure in topo II function [S. Mateos, I. Domínguez, N. Pastor, G. Cantero, F. Cortés, The DNA demethylating 5-azaC induces endoreduplication in cultured Chinese hamster cells, Mutat. Res. 578 (2005) 33-42]. The Chinese hamster mutant cell line EM9 has a high spontaneous frequency of endoreduplication as compared to its parental line AA8. In order to see if this is related to the degree of DNA methylation, we have investigated the basal levels of both endpoints in AA8 and EM9, as well as the effect of ext…
A microplate version of the DNA-synthesis inhibition test for rapid detection of DNA-alteration potentials.
1990
A microplate version of the DNA-synthesis inhibition test (DIT) for fast detection of DNA-alteration potentials has been developed. The DIT is based on the concept that DNA damage causes inhibition of DNA synthesis that becomes detectable some time after replicating cells have been in contact with genotoxic agents. In this test procedure human tissue culture cells (HeLa S3), prelabeled with [14C]thymidine, arfe exposed for 90 min to the substances in question. After the cells are rinsed, they are allowed to recover for 2 1/2 h in fresh culture medium, thereby unspecific interactions interfering with DNA replication are practically eliminated. Next, [3H]thymidine is added for 30 min, and the…
Chromosomal instability, reproductive cell death and apoptosis induced by O6-methylguanine in Mex−, Mex+ and methylation-tolerant mismatch repair com…
1998
O6-Methylguanine (O6-MeG) is induced in DNA by methylating environmental carcinogens and various cytostatic drugs. It is repaired by O6-methylguanine-DNA methyltransferase (MGMT). If not repaired prior to replication, the lesion generates gene mutations and leads to cell death, sister chromatid exchanges (SCEs), chromosomal aberrations and malignant transformation. To address the question of how O6-MeG is transformed into genotoxic effects, isogenic Chinese hamster cell lines either not expressing MGMT (phenotypically Mex-), expressing MGMT (Mex+) or exhibiting the tolerance phenotype (Mex-, methylation resistant) were compared as to their clastogenic response. Mex- cells were more sensitiv…
Mechanisms of quinolone resistance in Aeromonas species isolated from humans, water and eels.
2009
Mechanisms of resistance were determined in 33 quinolone-resistant isolates of the species Aeromonas hydrophila, Aeromonas caviae, Aeromonas media, Aeromonas salmonicida, Aeromonas popoffii and Aeromonas veronii, recovered from humans, freshwater and eels. The quinolone resistance-determining regions (QRDRs) of gyrA and parC genes were sequenced in these resistant strains, as well as in 8 quinolone-sensitive Aeromonas used as controls. All quinolone-resistant Aeromonas carried point mutations in the gyrA QRDR at codon 83, respectively giving rise to substitutions Ser(83)-->Ile (32 strains) or Ser(83)-->Val (1 strain). Almost half of these isolates (48%) carried additional point mutations in…
Spontaneous Quinolone Resistance in the Zoonotic Serovar of Vibrio vulnificus
2009
ABSTRACT This work demonstrates that Vibrio vulnificus biotype 2, serovar E, an eel pathogen able to infect humans, can become resistant to quinolone by specific mutations in gyrA (substitution of isoleucine for serine at position 83) and to some fluoroquinolones by additional mutations in parC (substitution of lysine for serine at position 85). Thus, to avoid the selection of resistant strains that are potentially pathogenic for humans, antibiotics other than quinolones must be used to treat vibriosis on farms.
Putrescine as a signal to modulate the indispensable ABA increase under cold stress.
2009
2 páginas -- PAGS nros. 219-220
Mutational Events in Cefotaximase Extended-Spectrum β-Lactamases of the CTX-M-1 Cluster Involved in Ceftazidime Resistance
2008
ABSTRACT CTX-M β-lactamases, which show a high cefotaxime hydrolytic activity, constitute the most prevalent extended-spectrum β-lactamase (ESBL) type found among clinical isolates. The recent explosive diversification of CTX-M enzymes seems to have taken place due to the appearance of more efficient enzymes which are capable of hydrolyzing both cefotaxime and ceftazidime, especially among the CTX-M-1 cluster. A combined strategy of in vitro stepwise evolution experiments using bla CTX-M-1 , bla CTX-M-3 , and bla CTX-M-10 genes and site-directed mutagenesis has been used to evaluate the role of ceftazidime and other β-lactam antibiotics in triggering the diversity found among enzymes belong…