| The rejoining of correct and incorrect DNA double-strand breaks (dsbs) ends was measured in non-cycling primary human fibroblast GM38 cells. I used standard pulsed-field gel electrophoresis techniques to show that radiation-induced dsbs are removed from the genome of GM38 cells with biphasic kinetics. By measuring the reconstitution of specific restriction fragments, I was able to determine that the fast repair component is a class of dsbs that rejoins correctly while the slow component is a class of dsbs that is subject to misrejoining. Also, Markov models showed that the dose response for dsb misrejoining is consistent with the idea that one class of dsbs is subject to misrejoining while another class of dsbs never misrejoins, regardless of the dose.; I studied dsb induction and repair in a number of different restriction fragments on human chromosome 11 of the CHO derived human-hamster hybrid A 1 cell to determine whether differences in dsb repair can account for the appearance of deletion breakpoint hotspots in CD59− mutants. Furthermore, I studied the induction and repair of dsbs in the same restriction fragments in GM38 cells to determine whether certain cellular factors influence dsb repair. I found no difference in either the induction, repair kinetics, or fidelity of repair of dsbs between the different restriction fragments or between the different cell lines.; GM38 cells were irradiated with particles of different LETs in the range of 7–190 keVμm to determine the effect of the initial pattern of energy deposition on DNA dsb induction, eurepair, and misrepair. The number of dsb clusters that remained unrejoined increased up to an LET of 100–150 keV/μm. A Markov model was developed to extrapolate to low doses DNA dsb misrejoining measurements made in the 20–160 Gy range. According to the model, the RBE for DNA dsb misrejoining is predicted to be dose dependent, with values as high as 20 for doses in the 0.5–1 Gy range and as low as 1 for doses greater than 40 Gy. |
