title: Cytotoxicity and SOS-inducing ability of ethidium and photoactivable analogs on E. coli ethidium-bromide-sensitive (Ebs) strains.
abstract: In a recently-characterized ethidium-bromide-sensitive E. coli strain, DNA appears to be much more accessible to DNA-binding agents. This strain therefore appears to be of interest for studying the mutagenic properties of chemicals. For this purpose, a series of ethidium-sensitive E. coli strains (Ebs) with normal and defective DNA-repair capacity was constructed and made lysogenic for lambda (sfiA::lacZ). These strains were used to study the cytotoxicity and SOS-inducing ability of ethidium and its two photoactivable analogs 8-azido- and 3,8-diazido-ethidium. When non-covalent DNA complexes are formed, these dyes elicit only a bacteriostatic effect in the Ebs strains, which is almost independent of the strain's DNA-repair capacity. The SOS system is not induced. When covalent DNA adducts are formed after photoactivation of ethidium azido analogs, the effects are quite different. The formation of about 5 DNA monoadducts per cell induces a lethal hit in the Ebs uvrB recA strain and measurable SOS induction in the Ebs uvrB (lambda (sfiA::lacZ) strain. The formation of more than 1000 DNA adducts in the Ebs strain with normal DNA-repair capacity does not induce any measurable cytotoxic effect.
mesh_terms: D001386:Azides / Q000494:pharmacology* / Q000528:radiation effects; D010582:Bacteriophage lambda / Q000187:drug effects; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004269:DNA, Bacterial / Q000187:drug effects* / Q000528:radiation effects; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D004996:Ethidium / Q000031:analogs & derivatives* / Q000494:pharmacology* / Q000528:radiation effects; D008433:Mathematics; D010777:Photochemistry; D013014:SOS Response, Genetics / Q000187:drug effects*; D014466:Ultraviolet Rays; D014775:Virus Activation / Q000187:drug effects
chemical_list: D001386:Azides; D004269:DNA, Bacterial; C030198:ethidium diazide; C014535:8-azidoethidium; D004996:Ethidium