DNA repair and cell repair: Are they related?

Abstract

Evidence of damage-repair processes is reviewed in connection with 3 types of cytotoxic cell treatments: X-radiation; far-ultraviolet (UV) (254 nm) light; and fluorescent light (FL) exposure of cells that had been grown in the presence of 5-bromodeoxyuridine (BUdR). In each case, the processes are characterized relative to cell survival and loss of DNA integrity, i.e. the presence of single-strand breaks evident under alkaline conditions and dimers containing thymine. From quantitative data of the induction of both types of end points, the number of DNA lesions are compared that are produced by a Do dose; that is, a dose that reduces survival by the factor 1 e (= 0.37). The number of single-strand breaks for the treatments BUdR/FL, X-rays, and far-UV are, respectively ∼50,000, ∼1,000, and ∼100. From such data, and upper-limit estimates of the persistence of breaks in X-irradiated surviving cells, it is concluded that: (1) X-ray survivors repair a large number of DNA lesions; and (2) X-ray lethality results from damage registered in a small fraction of the genome and/or the misrepair of supernumerary DNA lesions.