Luchnik A N, Bakaev V V
Mol Biol (Mosk). 1985 Jan-Feb;19(1):75-86.
The treatment of isolated SV40 mini-chromosomes by DNA-topoisomerase I leads to relaxation of DNA within a small fraction (2-5%) of mini-chromosomes strongly enriched in endogenous RNA-polymerase. The DNA supercoiling in the bulk of mini-chromosomes remained unchanged. The relaxable fraction proved to be specifically hypersensitive to DNAase I, but lost hypersensitivity after prior topoisomerase treatment. The DNA relaxation induced either by topoisomerase or DNAase I nicking and breaking led to almost a complete loss of proteins from this fraction while the DNA-protein interactions in the bulk of mini-chromosomes remained unchanged. Endogenous RNA-polymerase remained specifically enriched in these uncoated mini-chromosomes. It is concluded that (1) there is an elastic torsional strain in DNA within transcriptionally active mini-chromosomes, (2) DNA-protein interactions are altered within transcriptionally active mini-chromosomes, (3) there is evidence to indicate that local DNA conformational transitions in transcriptionally active chromatin are caused by DNA torsional strain.
用DNA拓扑异构酶I处理分离的SV40微型染色体，会使一小部分（2 - 5%）富含内源性RNA聚合酶的微型染色体中的DNA松弛。大部分微型染色体中的DNA超螺旋保持不变。可松弛部分被证明对DNA酶I具有特异性高敏感性，但在拓扑异构酶处理之前就失去了高敏感性。由拓扑异构酶或DNA酶I切口和断裂诱导的DNA松弛导致该部分的蛋白质几乎完全丢失，而大部分微型染色体中的DNA - 蛋白质相互作用保持不变。内源性RNA聚合酶仍特异性富集于这些未包被的微型染色体中。得出的结论是：（1）转录活性微型染色体中的DNA存在弹性扭转应变；（2）转录活性微型染色体中的DNA - 蛋白质相互作用发生改变；（3）有证据表明转录活性染色质中的局部DNA构象转变是由DNA扭转应变引起的。
