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REC A +‐DEPENDENT SYNERGISM BETWEEN 365 NM AND IONIZING RADIATION IN LOG‐PHASE ESCHERICHIA COLI: A MODEL FOR OXYGEN‐DEPENDENT NEAR‐UV INACTIVATION BY DISRUPTION OF DNA REPAIR
Author(s) -
Tyrrell Rex M.
Publication year - 1976
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1976.tb06764.x
Subject(s) - ionizing radiation , escherichia coli , pyrimidine dimer , dna , dna damage , mutant , irradiation , dna repair , oxygen , wild type , programmed cell death , chemistry , sos response , biophysics , biology , biochemistry , gene , apoptosis , physics , organic chemistry , nuclear physics
—The oxygen dependence of 365 nm inactivation of colony‐forming ability of Escherichia coli has been investigated in two series of DNA repair‐deficient K12 mutants grown to mid‐exponential phase. All strains except a uvr A rec A double mutant are more sensitive to inactivation under O 2 and show a lower threshold dose. The inactivation of photoreactivating enzyme in a crude cell extract and DNA repair disruption are both reduced when irradiation is carried out under nitrogen. The rec A gene‐dependent synergism between 365 nm and ionising radiation is reversible if cells are incubated in full growth medium before ionising radiation treatment. In a wildtype strain, incubation for 2.5 h in full growth medium after 10 6 J m ‐2 365 nm radiation changes a sensitised response to a protection from ionising radiation. Protection is not seen at 1.5 times 10 6 J m ‐2 . A tentative model for near UV lethality in logarithmic phase cells is suggested which proposes two classes of lesions. One requires oxygen for it's induction, is rapidly fixed as a lethal event as a result of repair disruption, and is primarily responsible for cell death after aerobic 365 nm irradiation. The other lesion, possibly pyrimidine dimers, may lead to cell death under anaerobic conditions.