Parshad R, Tarone R E, Price F M, Sanford K K
Pathology Department, Howard University College of Medicine, Washington, DC 20059.
Mutat Res. 1993 Aug;294(2):149-55. doi: 10.1016/0921-8777(93)90023-a.
The capacity of cells to incise DNA to remove altered sites after DNA damage can be determined from the rate of DNA-strand break accumulation in the presence of an inhibitor of DNA-repair synthesis, such as 1-beta-D-arabinofuranosylcytosine (ara-C). Because each chromatid contains a single continuous molecule of double-stranded DNA, chromatid breaks and gaps, i.e., non-displaced breaks, represent unrepaired DNA-strand breaks. The accumulation of chromatid breaks and gaps after X-irradiation in the presence of ara-C thus provides a measure of DNA incision activity. Addition of ara-C to skin fibroblasts or stimulated blood lymphocytes from normal individuals at intervals after X-irradiation significantly increased frequencies of chromatid breaks and/or gaps. In contrast, addition of ara-C to XP cells of complementation groups A and D had a negligible effect and a significant but less than normal effect on XP cells of complementation group C and one sample of blood lymphocytes of undetermined complementation group. The results thus show negligible incision activity after G2 phase X-irradiation in XP-A and XP-D cells and a level higher but less than normal in XP-C cells.
细胞在DNA损伤后切割DNA以去除改变位点的能力，可以通过在DNA修复合成抑制剂（如1-β-D-阿拉伯呋喃糖基胞嘧啶，ara-C）存在的情况下DNA链断裂积累的速率来确定。由于每条染色单体包含一个双链DNA的单一连续分子，染色单体断裂和间隙，即未移位的断裂，代表未修复的DNA链断裂。因此，在ara-C存在的情况下，X射线照射后染色单体断裂和间隙的积累提供了一种衡量DNA切割活性的方法。在X射线照射后的不同时间间隔，向正常个体的皮肤成纤维细胞或刺激的血液淋巴细胞中添加ara-C，显著增加了染色单体断裂和/或间隙的频率。相比之下，向互补组A和D的XP细胞中添加ara-C的影响可忽略不计，而向互补组C的XP细胞和一个未确定互补组的血液淋巴细胞样本中添加ara-C则有显著但低于正常水平的影响。因此，结果表明，XP-A和XP-D细胞在G2期X射线照射后的切割活性可忽略不计，而XP-C细胞中的切割活性水平较高但低于正常水平。
