Studies on the Radiation-Induced Breakdown of Deoxyribonucleic Acid in Escherichia coli 15 T - L -

Abstract

A study of the breakdown of DNA in L. coli 15 T-L- following [gamma]-irradiation has shown that the initiation of degradation requires radiation action within the cell and the expression of degradation following the irradiation is dependent of postirradiation environmental conditions. DNA degradation is initiated only after direct irradiation and not by suspension in irradiated medium. The fact that degradation appears independent of temperature between 30[degree]Cand 41 [degree]C suggests that the mechanism of degradation may be the same as, or related to, thatof DNA synthesis. Post-irradiation incubation with 0.2 M ammonium acetate inhibits degradation. Returning the cells to growth medium results in degradation, but the maximum degraded is less, suggesting that some, but not all, of the lesions are removed in the ammonium acetate. Cells growing in medium with succjnate rather than glucose as the energy source are more sensitive to degradation. Enhancement of degradation by inhibiting protein synthesis or by bubbling with nitrogen suggests that a cytoplasmic change may occur which makes the DNA more sensitive to the degradation process. Autoradiography indicates that degradation does not vary from one cell to another, and thin-layer chromatographic studies indicate that thymine is lost into the medium during degradation.