Käs E, Laemmli U K
Department of Biochemistry, University of Geneva, Switzerland.
EMBO J. 1992 Feb;11(2):705-16. doi: 10.1002/j.1460-2075.1992.tb05103.x.
We have identified two classes of in vivo topoisomerase II cleavage sites in the Drosophila histone gene repeat. One class co-localizes with DNase I-hypersensitive regions and another novel class maps to a subset of consecutive nucleosome linker sites in the scaffold-associated region (SAR) of the histone gene loop. Prominent topoisomerase II cleavage is also observed in one of the linker regions of the two nucleosomes spanning satellite III, a centromeric SAR-like DNA sequence with a repeat length of 359 bp. At the sequence level, in vivo topoisomerase II cleavage is highly site specific. Comparison of 10 nucleosome linker sites defines an in vivo cleavage sequence whose major characteristic is a prominent GC-rich core. These GC-rich cleavage sites are flanked by extensive arrays of oligo(dA).oligo(dT) tracts characteristic of SAR sequences. Treatment of cells with distamycin selectively enhances cleavage at nucleosome linker sites of the SAR and satellite regions, suggesting that AT-rich sequences flanking cleavage sites may be involved in determining topoisomerase II activity in the cell. These observations provide evidence for the association of topoisomerase II with SARS in vivo.
我们已经在果蝇组蛋白基因重复序列中鉴定出两类体内拓扑异构酶II切割位点。一类与DNase I超敏区域共定位，另一类新的位点定位于组蛋白基因环的支架相关区域（SAR）中连续核小体连接位点的一个子集。在跨越卫星III的两个核小体的一个连接区域中也观察到显著的拓扑异构酶II切割，卫星III是一种着丝粒SAR样DNA序列，重复长度为359 bp。在序列水平上，体内拓扑异构酶II切割具有高度的位点特异性。对10个核小体连接位点的比较确定了一个体内切割序列，其主要特征是一个突出的富含GC的核心。这些富含GC的切割位点两侧是SAR序列特有的大量寡聚（dA）·寡聚（dT）片段阵列。用distamycin处理细胞可选择性增强SAR和卫星区域核小体连接位点的切割，这表明切割位点两侧富含AT的序列可能参与确定细胞中拓扑异构酶II的活性。这些观察结果为体内拓扑异构酶II与SARS的关联提供了证据。
