Far and Near Ultraviolet Light as Molecular Probes for Assessment of DNA Repair and Radiosensitivity
In previous lectures I have described the effects of radiation on cells and cell constituents, the methods of evaluating the damage and the photo- and radiation- products which are responsible for the damage, and lead to either cell death or, what is sometimes worst, to mutation. For reasons of space and scope there will be no attempt to repeat in detail the description of these effects, and the details may be read in the outstanding presentation of B. Sutherland (1), and of Riklis (2), as well as in the different papers in this volume dealing with cellular repair mechanisms. If massive assaults by radiation or other damaging agents may be recognized easily and measured simply by survival curves, damage to the most sensitive cellular constituent, DNA, requires biochemical methods of detection. The lymphocyte, being the most sensitive cell, provided the necessary object for studying effects, by cytogenetical methods, but chromosome aberrations may be the end result of a series of biochemical events, among them the most important is the existence of molecular repair mechanisms, and it is the capacity of repair which dictates the fate of an irradiated cell. The phenomena of repair have become far more complicated than when excision repair was first discovered in 1963 (3,4,5). Not only repair capacity, but also repair fidelity determine the ultimate fate of the cell and organism: excision repair and photoreactivation are error-free, but other mechanisms such as postreplication-recombination, and the recently discovered SOS repair are error-prone, thus increasing the chance of mutation and carcinogenicity. In this respect, low-level radiation becomes more disturbing as its effects are not resulting so much in cell death as in cell mutation.
KeywordsRepair Capacity Xeroderma Pigmentosum Label Thymidine Repair Synthesis Photoallergic Reaction
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