Turner G N, Nobis P, Dewey W C
Biophys J. 1976 Sep;16(9):1003-12. doi: 10.1016/S0006-3495(76)85751-7.
The DNA in Chinese hamster cells was labeled first for 3 h with [3H]TdR and then for 3 h with [125I]UdR. Chromatin was extracted, frozen, and stored at -30 degrees C until 1.0 X 10(17) and 1.25 X 10(17) disintegrations/g of labeled DNA occurred for 125I and 3H respectively. Velocity sedimentation of chromatin (DNA with associated chromosomal proteins) in neutral sucrose gradients indicated that the localized energy from the 125I disintegrations, which gave about 1 double-strand break/disintegration plus an additional 1.3 single strand breaks, selectively fragmented the [125I] chromatin into pieces smaller than the [3H] chromatin. In other words, 125I disintegrations caused much more localized damage in the chromatin labeled with 125I than in the chromatin labeled with 3H, and fragments induced in DNA by 125I disintegrations were not held together by the associated chromosomal proteins. Use of this 125I technique for studying chromosomal proteins associated with different regions in the cellular DNA is discussed. For these studies, the number of disintegrations required for fragmenting DNA molecules of different sizes is illustrated.
先用[³H]胸苷标记中国仓鼠细胞中的DNA 3小时，然后用[¹²⁵I]尿苷标记3小时。提取染色质，冷冻，并储存在-30℃，直到分别发生1.0×10¹⁷和1.25×10¹⁷次衰变/克标记DNA（¹²⁵I和³H分别达到此衰变次数）。在中性蔗糖梯度中对染色质（带有相关染色体蛋白的DNA）进行速度沉降分析表明，¹²⁵I衰变产生的局部能量（约每一次衰变产生1个双链断裂加上额外的1.3个单链断裂）选择性地将[¹²⁵I]染色质片段化，形成比[³H]染色质更小的片段。换句话说，¹²⁵I衰变在¹²⁵I标记的染色质中造成的局部损伤比在³H标记的染色质中多得多，并且¹²⁵I衰变在DNA中诱导产生的片段不会被相关的染色体蛋白维系在一起。本文讨论了使用这种¹²⁵I技术来研究与细胞DNA不同区域相关的染色体蛋白。对于这些研究，还说明了使不同大小的DNA分子片段化所需的衰变次数。
