Studies on Ultraviolet Irradiation of Escherichia coli Containing 5-Bromouracil in its DNA

Abstract

Surgeons, New Ymk, U.S.A.SUMMARY: Thymine-requiring Escherichia coZi 15, t-and E. coli B, t-which contained 5-bromouracil in their deoxyribonucleic acid in place of thymine showed a marked increase in sensitivity to ultraviolet (u.v.) radiation. The effect was proportional to the extent of incorporation of 5-bromouracil under defined growth conditions and for a given medium. This increase in sensitivity to U.V. was not hereditary.A maximum U.V. dose-increase effect on survival of 3.5 was obtained ; there was as high as a 20,000-fold decrease in the number of survivors as compared to irradiated bacteria grown in absence of the analogue. This effect was not obtained with bacteria grown before irradiation in 2-thiothymine (an inhibitor not incorporated into DNA), nor was there an increase in U.V. sensitivity in organisms grown under conditions of thymine starvation or of 5-flurouracil inhibition. Furthermore, bacteria which did not require thymine and did not incorporate 5-bromouracil did not show this sensitization effect. The increase in U.V. sensitivity caused by 5-bromouracil was annulled by thymine. 5-Iodouracil caused a lower increase in u.v.-sensitization. The extent of photo-reactivation was not as great in irradiated bacteria which had been grown in 5-bromouracil as in bacteria containing no analogue in their DNA. A u.v.-resistant mutant of E. coli 15, t-was isolated and found to be affected by 5-bromouracil in a manner similar to the slightly more u.v.-sensitive parent strain. Incorporation of 5-bromouracil did not result in a dose-increase effect on u.v.-induced mutagenesis at the thymine-dependent locus of E. coli 15, t-. Bacteria containing 5-bromouracil were similarly hypersensitive to heat but showed no increased sensitivity to H,O, and several nitrogen mustards.

Restoration of 5-Bromouracil-sensitized Escherichia coli Strain B after Exposure to Ionizing or Ultraviolet Radiation

“…Therefore it may be that the same type of damage is enhanced by the one agent and restored by the other. Although no direct examination was made of the location of the 5-BU in the E. coli B used here it seems clear from observations by other workers (Greer, 1960; Kaplan, Smith & Tomlin, 1962) that radiationsensitization only occurs when 5-BU replaces some of the thymine in the DNA. Thus the location of this lesion can be defined and it seems reasonable to suppose that treatment with chloramphenicol decreases the expression of some of this damage in DNA.…”

“…irradiated 5-BU bacteria can be restored to such a marked degree by treatment with chloramphenicol, because reports by other authors have indicated that photo-reactivation of bacteria or bacteriophage which contain 5-BU or 5-bromodeoxyuridine (5-BUDR) is prevented or markedly decreased (Greer, 1960; Lorkiewitz & Szybalski, 1960; Stahl et al 1961). Host cell reactivation of phage T 1 which contained 5-BUDR is also much diminished (Sauerbier, 1961 ; Howard-Flanders, Boyce & Theriot, 1962).…”

“…The strain B of Escherichia coti was the same as that used in previous work (Alper & Gillies, 1958, 1960Gillies & Alper, 1959). It was maintained on slopes of Oxoid nutrient agar stored at 4 ' .…”

The Recombination of Bromouracil-containing Deoxyribonucleic Acid in Salmonella typhimurium Transduction

“…The presence of BU in DNA increases the sensitivity of bacteria to the lethal effects of ultraviolet radiation (Greer, 1960;Fig. I).…”

Biochemical and Genetical Studies on Radioresistant Mouse Cells in Culture

“…It was shown by Greer (1960), Djordjevic and Szybalski (1960) and Aoyama et al (1964) that the incorporation of 5-bromodeoxyuridine into cells greatly enhanced their Aoyama et al (1964) to be the most effective for radiosensitization in either kinds of cells (Fig. 7).…”