PROTECTION OF ESCHERICHIA COLI CELLS AGAINST THE LETHAL EFFECTS OF ULTRAVIOLET AND X IRRADIATION BY PRIOR X IRRADIATION: A GENETIC AND PHYSIOLOGICAL STUDY

Authors

  • Kendric C. Smith,

    1. Department of Radiology, Stanford University School of Medicine, Stanford, CA 94305, U.S.A.
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  • Klaus D. Martignoni

    1. Department of Radiology, Stanford University School of Medicine, Stanford, CA 94305, U.S.A.
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    • *Strahlenbiologisches Institut der Universitat München, 8 München 2, Bavariaring 19, W. Germany.


Abstract

Abstract— When log phase cells of wild-type E. coli K-12 were maintained in growth medium after X irradiation, they became progressively more resistant to a subsequent exposure to UV or X radiation. The time to achieve maximum resistance was about 60 min. The uvrB, uvrD, polA and certain exrA strains (W3110 background) also demonstrated this X ray-induced resistance to subsequent UV or X irradiation but recA, recB, lex (AB1157 or W3110 backgrounds) and other exrA strains (AB1157 background) did not. The resistance induced in wild-type, uvrB and uvrD cells was characterized by the production or enhancement of a shoulder on the survival curves obtained for the second irradiation, while the resistance induced in the W3110 exrA strains was expressed only as a change in slope. The induction of resistance in the W3110 exrA strain was not inhibited by the presence of chloramphenicol, but that in the wild-type cells appeared to be. The production or enhancement of a shoulder on the survival curves of the rec+lex+exr+ cells is consistent with the concept of the radiation induction of repair enzymes. Alternative explanations, however, are discussed.

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