DNA SUPERCOILING CHANGES AND NUCLEOID PROTEIN-COMPOSITION IN A GROUP OF L5178Y CELLS OF VARYING RADIOSENSITIVITY

Cells of the radioresistant L5178Y-R, -S35, -SR and M10(neo 5)-1 and r adiosensitive L5178Y-S, M10 and LX830 cell lines were used to investig ate the relationship between radiosensitivity and DNA supercoiling abi lity mediated by the nuclear matrix within chromatin loops containing DNA damage. The ability of DNA loops to undergo changes in supercoilin g in the presence of radiation-induced damage revealed that in all cas es the degree of inhibition of supercoil rewinding was greater in the radiosensitive cells. Since the amount of DNA damage induced per unit dose is known to be equal in all these cell lines, the same number of DNA lesions produced a greater loss of topological constraint in the r adiosensitive cells. The differential loss of DNA supercoiling ability could be due to differences in DNA-nuclear matrix anchor points. High -resolution two-dimensional gel electrophoresis of nucleoid proteins s howed numerous reproducible differences in nuclear matrix protein betw een the cell lines studied, A total of nine proteins were associated w ith nucleoids from L5178Y-R cells and absent from L5178Y-S nucleoids, None of them, however, correlated absolutely with radioresistance, Thu s, unlike previous studies in CHO cells no candidates for the conveyan ce of cellular radiosensitivity that were single proteins were detecte d. However, these results are consistent with the hypothesis that stab ility of DNA loop domains in the presence of DNA damage is a determina nt of the outcome of radiation-induced DNA damage. (C) 1996 by Radiati on Research Society