Introduction of a UV-damaged replicon into a recipient cell is not a sufficient condition to produce an SOS-inducing signal.
Three models have been proposed for the nature of the SOS-inducing signal in E. coli. One model postulates that degradation products of damaged DNA generate an SOS-inducing signal; another model surmises that the very lesions produced by UV damage constitute the SOS-inducing signal in vivo; a third model proposes that DNA damage is processed upon DNA replication to form single-stranded DNA (the SOS signal) that activates RecA protein. We tested the models by measuring SOS induction produced by introducing into recipient cells the UV-damaged DNA of 2 constructed phagemids. We used phagemids since they transferred DNA to the recipients with 100% efficiency. The origin of replication of the phagemids was either oriC from the E. coli chromosome, or oriF from F plasmid. Replication of the oriC phagemid was dependent on methylation. A UV-damaged oriC phagemid failed to induce SOS functions in a recipient cell whereas an oriF phagemid did induce them. Our results disprove the first and the second model proposed for the nature of the SOS-inducing signal. The failure of a UV-damaged oriC replicon to induce SOS can be explained by the third model if one assumes that replication of a UV-damaged oriC plasmid does not generate single-stranded DNA as does the E. coli chromosome after UV damage.
Sommer
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S
Groupe d'Etude de la Mutagénèse et de la Cancérogénèse, Laboratoire d'Enzymologie, CNRS, Gif-sur-Yvette, France.
Leitaõ
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A
Bernardi
A
A
Bailone
A
A
Devoret
R
R
D010582:Bacteriophage lambda / Q000235:genetics; D004247:DNA / Q000528:radiation effects; D004249:DNA Damage / Q000502:physiology; D004261:DNA Replication; D004274:DNA, Recombinant; D004277:DNA, Single-Stranded / Q000096:biosynthesis; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D008745:Methylation; D008780:Methyltransferases; D008957:Models, Genetic; D010957:Plasmids / Q000235:genetics; D011938:Rec A Recombinases / Q000096:biosynthesis; D012093:Replicon; D013014:SOS Response, Genetics; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D014466:Ultraviolet Rays
D004274:DNA, Recombinant; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D004247:DNA; D008780:Methyltransferases; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C499294:dam protein, E coli; D011938:Rec A Recombinases