Warters R L, Lyons B W
Department of Radiology, University of Utah Health Sciences Center, Salt Lake City 84132.
Radiat Res. 1993 Jun;134(3):337-42.
The induction and closure of double-strand breaks produced by X rays were measured in the replicating DNA of HeLa S3 cells using the techniques of neutral (pH 7.2) filter elution and pulsed-field agarose gel electrophoresis. In whole cell DNA the apparent yield of double-strand breaks in pulse-labeled DNA was approximately half that observed in bulk DNA as estimated by both techniques. In contrast, when nuclear DNA was reduced to sub-replicon-cluster lengths prior to irradiation, the yield of radiation-induced double-strand breaks was the same in both replicating and bulk DNA. During incubation of pulse-labeled whole cells at 37 degrees C, the sensitivity of pulse-labeled DNA to strand break induction approached that observed in bulk DNA with a half-time of approximately 105 min. The results indicate that double-strand breaks are produced at a similar frequency per DNA mass in both replicating and bulk DNA. The structure of replicating DNA obscures length reduction in whole cell DNA when estimated by either filter elution or gel electrophoresis. Closure of double-strand breaks proceeded at a similar rate in both replicating and bulk DNA.
利用中性（pH 7.2）滤膜洗脱技术和脉冲场琼脂糖凝胶电泳技术，对HeLa S3细胞复制性DNA中由X射线产生的双链断裂的诱导和封闭进行了测量。在全细胞DNA中，通过两种技术估算，脉冲标记DNA中双链断裂的表观产量约为总体DNA中观察到的产量的一半。相比之下，当在照射前将核DNA缩短至亚复制子簇长度时，复制性DNA和总体DNA中辐射诱导的双链断裂产量相同。在37℃孵育脉冲标记的全细胞期间，脉冲标记DNA对链断裂诱导的敏感性以约105分钟的半衰期接近总体DNA中观察到的敏感性。结果表明，在复制性DNA和总体DNA中，每单位DNA质量产生双链断裂的频率相似。当通过滤膜洗脱或凝胶电泳估算时，复制性DNA的结构掩盖了全细胞DNA中的长度减少。双链断裂的封闭在复制性DNA和总体DNA中以相似的速率进行。
