RESUMO
The SOS response is a universal bacterial regulon involved in the cellular response to DNA damage and other forms of stress. In Caulobacter crescentus, previous work has identified a plethora of genes that are part of the SOS regulon, but the biological roles of several of them remain to be determined. In this study, we report that two genes, hereafter named mmcA and mmcB, are involved in the defense against DNA damage caused by mitomycin C (MMC), but not against lesions induced by other common DNA damaging agents, such as UVC light, methyl methanesulfonate (MMS) and hydrogen peroxide. mmcA is a conserved gene that encodes a member of the glyoxalases/dioxygenases protein family, and acts independently of known DNA repair pathways. On the other hand, epistasis analysis showed that mmcB acts in the same pathway as imuC (dnaE2), and is required specifically for MMC-induced mutagenesis, but not for that induced by UV light, suggesting a role for MmcB in translesion synthesis-dependent repair of MMC damage. We show that the lack of MMC-induced mutability in the mmcB strain is not caused by lack of proper SOS induction of the imuABC operon, involved in translesion synthesis (TLS) in C. crescentus. Based on this data and on structural analysis of a close homolog, we propose that MmcB is an endonuclease which creates substrates for ImuABC-mediated TLS patches.
Assuntos
Proteínas de Bactérias/genética , Caulobacter crescentus/genética , Genes Bacterianos , Mitomicina/farmacologia , Resposta SOS em Genética/genética , Sequência de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Sequência de Bases , Domínio Catalítico , Caulobacter crescentus/efeitos dos fármacos , Caulobacter crescentus/crescimento & desenvolvimento , Caulobacter crescentus/efeitos da radiação , Sequência Conservada , Dano ao DNA , Farmacorresistência Bacteriana/efeitos dos fármacos , Farmacorresistência Bacteriana/genética , Epistasia Genética/efeitos dos fármacos , Epistasia Genética/efeitos da radiação , Deleção de Genes , Viabilidade Microbiana/efeitos dos fármacos , Viabilidade Microbiana/efeitos da radiação , Modelos Moleculares , Dados de Sequência Molecular , Mutagênese/efeitos da radiação , Mutação/genética , Taxa de Mutação , Fenótipo , Regiões Promotoras Genéticas/genética , Resposta SOS em Genética/efeitos dos fármacos , Resposta SOS em Genética/efeitos da radiação , Raios UltravioletaRESUMO
Se estudiaron los daños primarios producidos por la radiación gamma en el ADN de cepas de Escherichia coli portadoras de la fusión génica sulA::lacZ y de mutaciones en diferentes genes de reparación del ADN. Además, se determinó su radiosensibilidad. Las cepas con mutaciones en los genes recN y uvrA fueron más sensibles que la tipo salvaje. Esto concuerda con estudios previos donde se demostró que los genes rec y uvr participaban en la reparación del daño en el ADN producido por los rayos gamma. En las cepas mutantes se encontraron diferencias significativas en los niveles de expresión del gen sulA en relación con el tipo salvaje. Se discute la utilidad de las cepas estudiadas como biosensores de genotoxicidad así como en estudios de radioprotección
Assuntos
Dano ao DNA , Reparo do DNA , Escherichia coli , Raios gama , Resposta SOS em Genética/efeitos da radiaçãoRESUMO
The effect of sodium diethyldithiocarbamate (DDC) and S-2-aminoethyl-isothiouronicadenosin-5-triphosphate (adeturon) in the induction of Escherichia coli SOS response promoted by gamma-irradiation was studied by measuring the induction of sulA gene and the induction of lambda prophage. Furthermore, as a way of measure the exonuclease activity in gamma-irradiated cells in the presence or absence of both compounds, the DNA degradation was determined. Adeturon did not affected DNA degradation, but inhibited the induction of the SOS functions studied. On the contrary, DDC inhibited DNA degradation as well as the induction of the sulA gene, but enhanced lambda induction in E. coli lysogenic strains. These results indicate that both compounds diminish the DNA damage produced by gamma-irradiation and also suggest that the mechanisms of radioprotection must be different. Thus, radioprotection mediated by DDC should involve free hydroxyl radical scavenging and a minor activity of exonuclease. The enhancement of phage induction in E. coli cells that DDC produces could be attributed to its quelant effect and this would not be not probably directly related to radioprotection. Adeturon, as thiols, may serve also as scavenging agent of free hydroxyl radicals, diminishing indirectly the DNA damage level. In addition, adeturon must interact with DNA in the same form that other aminothiol compounds do it. This interaction, mediated by amino groups of adeturon, may serve to concentrate these compounds near of the DNA damage site, increasing the potential for the thiol portion of the molecule to donate hydrogen, decreasing the damage level on DNA molecule. However, adeturon do not modify the exonuclease activity. Some topic about the possible clinical application of both compounds are discussed.