Showing papers by "Giustina Simone published in 1973"

DNA Repair and Degradation in X-irradiated E. Coli B/r Cells after Treatment with Ultra-violet Light and N-ethylmaleimide

Abstract: A study was made of the effect of 5 x 10/sup -4/M N-ethylmaleimide (NEM) on the survival of Escherichia coli cells that had or had not been previously exposed to ultraviolet radiation at 600 or 1200 ergs/mm/sup 2/ before irradiation with x rays in suspensions saturated with air or nitrogen. The dose range of the x rays was 0 to 70 Krads. The enhancement by ultraviolet of the response to x rays in air was slightly more pronounced in Ni. NEM sensitized control cells to a greater extent in anoxia, but in air had practically no effect on cells previously exposed to 600 ergs/mm/sup 2/, and actively protected cells previously exposed to 1200 ergs/mm/sup 2/. In N/sub 2/, the results concerning cells previously exposed to uv light were qualitatively the same as in air, but significantly less evident. ln air the protective effect of NEM was reduced by ~40% in cells photoreactivated after exposure to 1200 ergs/mm/sup 2/ of uv light, and before the addition of NEM and x irradiation. In N/sub 2/, the sensitizing activity of the drug was partially restored by photoreactivation. In the presence of NEM, it was shown that a greater number of single-strand DNA breaksmore » was produced immediately after x irradiation. These were repaired out at a slower rate than under control conditions (30% versus 65% of breaks repaired in 80 min). In cells exposed only to uv light, there was no evidence of single- strand breaks immediately after exposure, but they appeared after incubation and were repaired to about 60% after 40 min. In cells exposed to uv and then to x rays, the number of breaks immediately after irradiation appeared to be the same as in those treated only with x rays, but after 40 and 80 min there was evidence of extensive DNA degradation with no repair. In the combined treatment with uv, NEM, and x rays, the number of breaks immediately after irradiation corresponded to that of samples treated with NEM and x rays, with a slow but significant repair taking place. (UK)« less