RESUMO
In Escherichia coli cells, an increase in temperature induces immediate DNA relaxation, followed by the fast recovery of DNA supercoiling. DNA gyrase, proteins synthesized during heat stress, and chaperone DnaK have been proposed to participate in this recovery. However, the mechanism of DNA supercoiling recovery has not been completely elucidated. The results presented here suggest that in cells exposed to severe heat-shock stress, DNA supercoiling levels are recovered by the reactivation of DNA gyrase. This reactivation involves solubilization of a fraction of protein GyrA present in protein aggregates, by the bichaperone DnaK-ClpB system.
Assuntos
DNA Girase/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/fisiologia , Proteínas de Choque Térmico/metabolismo , Resposta ao Choque Térmico/fisiologia , Chaperonas Moleculares/metabolismo , DNA Super-Helicoidal/metabolismo , Endopeptidase Clp , Escherichia coli/genética , Escherichia coli/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Choque Térmico HSP70/genética , Proteínas de Choque Térmico HSP70/metabolismo , Proteínas de Choque Térmico/genética , Chaperonas Moleculares/genéticaRESUMO
In RecBCD(+) cells, a mutated single-strand DNA 3'-5' exonuclease ExoI (SbcB15) induced an increase in stationary-phase mutation. In sbcB15 cells, as in wild-type cells, these mutations partially required RecA, RecB, RecF, and expression of the LexA regulon. The absence of nuclease SbcCD in sbcB15 cells decreased stationary-phase mutation and induced an increase in the number of cell filaments. The absence of ExoI (Deltaxon) in wild-type or sbcC cells did not change significantly the stationary-phase mutation. Differences between the sbcB15 and DeltaxonA cells suggest a correlation between level of SOS induction and the generation of stationary-phase mutations.
Assuntos
Desoxirribonucleases/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/enzimologia , Escherichia coli/genética , Exodesoxirribonucleases/metabolismo , Exonucleases/metabolismo , Mutação , Desoxirribonucleases/genética , Escherichia coli/crescimento & desenvolvimento , Proteínas de Escherichia coli/genética , Exodesoxirribonucleases/genética , Exonucleases/genéticaRESUMO
The ccd system of the F plasmid encodes CcdB, a protein toxic to DNA-gyrase, and CcdA, its antitoxin. The function attributed to this system is to contribute to plasmid stability by killing bacteria that lose the plasmid during cell division. However, the function of ccd in resting bacteria is not clear. Results presented show that ccd transcription increases as bacteria enter stationary phase and that the amount of the Ccd proteins is higher in bacteria under nutritional stress than in growing bacteria. Moreover, an increase in the frequency of Lac+ "adaptive" mutations was observed in stationary-phase bacteria that over-express the Ccd proteins.
Assuntos
Proteínas de Bactérias/metabolismo , Toxinas Bacterianas/metabolismo , Citotoxinas/metabolismo , Escherichia coli/fisiologia , Proteínas de Bactérias/genética , Meios de Cultura , Proteínas de Escherichia coli/genética , Mutação da Fase de Leitura , Óperon Lac/genética , Lactose , Mutação , Fator sigma/genéticaRESUMO
When nutrients become scarce E. coli cells enter into a non-growth phase known as stationary and develop a multiple-stress resistance state analogue to sporulation in B. subtilis. Morphological changes are observed, including rounded shape, loss of flagella and thickening of the cell wall. General metabolism is redirected, macromolecular degradation is increased, and storage and osmoprotection compounds are synthesized. The reorganization of the nucleoid is accompanied by an overall repression of gene expression, but a subset of genes required for starvation survival become transcribed in a manner dependent on the stationary phase-specific subunit of RNA polymerase (RpoS or sigma(s)). The regulatory function of sigma(s) seems to be central to a global gene network that is beginning to be understood. Also, stationary phase populations are highly heterogeneous in properties as viability, genotype, and mutability. The emergence of mutant subpopullations capable of using nutrient traces suggest survival strategies during long term starvation. This review focuses on the major characteristics of E. coli during stationary phase and on the regulatory gene network responsible of such characteristics.
Assuntos
Escherichia coli/crescimento & desenvolvimento , Proteínas de Bactérias/fisiologia , DNA Bacteriano/genética , Escherichia coli/citologia , Escherichia coli/genética , Escherichia coli/metabolismo , Proteínas de Escherichia coli/fisiologia , Regulação Bacteriana da Expressão Gênica/fisiologia , Genes Bacterianos , Fator sigma/fisiologia , Transcrição GênicaRESUMO
Stationary-phase cells displayed a distribution of relaxed plasmids and had the ability to recover plasmid supercoiling as soon as nutrients became available. Preexisting gyrase molecules in these cells were responsible for this recovery. Stationary-phase rpoS cells showed a bimodal distribution of plasmids and failed to supercoil plasmids after the addition of nutrients, suggesting that rpoS plays a role in the regulation of plasmid topology during the stationary phase.