Studies on sister chromatid exchange (SCE) induction by gamma-irradiation and protective effect of L-cysteine in HeLa cells.

Effect of different doses of gamma-irradiation on SCE induction in unifiliarly 5-bromo 2-deoxyuridine substituted DNA was studied in various phases of cell cycle. Changes in gamma-irradiation induced SCE frequency was measured by post-irradiation treatment with antimutagen L-cysteine. Perturbation in cellular proliferation kinetics due to gamma-irradiation and gamma-irradiation plus L-cysteine was also studied. It was observed that gamma-irradiation is an efficient inducer of SCE and is most effective in S phase. L-cysteine also causes SCE induction which is slightly higher than the spontaneous level of SCEs found in HeLa cells. However, post-irradiation addition of L-cysteine reduces SCE frequency in gamma-irradiated cultures and this reduction is maximum in G1 phase irradiated cells. gamma-irradiation delayed the mitosis considerably and this delay continued to increase with increasing doses. L-cysteine reduced the delay in cell cycle caused by gamma-irradiation.