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A simple, inexpensive, and sensitive test for potential carcinogens based upon the property of carcinogens to induce prophage lambda is described. By using chemicals activated with microsomal enzymes and E. coli K12 permeable (envA) tester bacteria also deficient in DNA repair (uvrB), the range of carcinogens detected in a lysogenic induction test(More)
Plasmid R6-5 contains a locus whose product inhibits induction of sfiA and prophage lambda in a recA441 mutant at 42 degrees C and in a recA+ host after treatment with nalidixic acid. This plasmidic SOS-inhibition locus (psi) is situated on an 8.1-kilobase DNA fragment near oriT, the origin of plasmid R6-5 conjugational transfer. Loss of the Psi function,(More)
The UmuD'C mutagenesis complex accumulates slowly and parsimoniously after a 12 Jm(-2) UV flash to attain after 45 min a low cell concentration between 15 and 60 complexes. Meanwhile, RecA monomers go up to 72,000 monomers. By contrast, when the UmuD'C complex is constitutively produced at a high concentration, it inhibits recombinational repair and then(More)
We further characterize a novel plasmid function preventing SOS induction called Psi (Plasmid SOS Inhibition). We show that Psi function is expressed by psiB, a gene located at coordinate 54.9 of plasmid R6-5 and near oriT, the origin of conjugal transfer. Deletions and amber mutations of the psiB gene permitted us to demonstrate that PsiB polypeptide(More)
We have characterized the mismatch repair system (MMR) of the highly radiation-resistant type strain of Deinococcus radiodurans, ATCC 13939. We show that the MMR system is functional in this organism, where it participates in ensuring the fidelity of DNA replication and recombination. The system relies on the activity of two key proteins, MutS1 and MutL,(More)
Mutants of the cI gene of prophage lambda have been defined phenotypically in a recA+ host as noninducible (Ind-), inducible (Ind+), or induction sensitive (Inds). We showed that a phage lambda cI+ carrying operator mutations v2 and v3 displays an Inds phenotype, as does lambda cI inds-1. We characterized a fourth induction phenotype called induction(More)
Dehydration or desiccation is one of the most frequent and severe challenges to living cells. The bacterium Deinococcus radiodurans is the best known extremophile among the few organisms that can survive extremely high exposures to desiccation and ionizing radiation, which shatter its genome into hundreds of short DNA fragments. Remarkably, these fragments(More)
To isolate strains with new recA mutations that differentially affect RecA protein functions, we mutagenized in vitro the recA gene carried by plasmid mini-F and then introduced the mini-F-recA plasmid into a delta recA host that was lysogenic for prophage phi 80 and carried a lac duplication. By scoring prophage induction and recombination of the lac(More)
Escherichia coli cells induced for the SOS response express inducible stable DNA replication (iSDR) as an SOS function. Initiation of iSDR is independent of transcription, translation and DnaA protein, which are essential for initiation of DNA replication from oriC. We found that a recA mutant that is defective in recombination but proficient in SOS(More)