Bakayev V V, Yugai A A, Luchnik A N
Nucleic Acids Res. 1985 Oct 11;13(19):7079-93. doi: 10.1093/nar/13.19.7079.
The effect of X-irradiation on DNAase I hypersensitivity of SV40 minichromosomes within nuclei or free in solution was investigated. The susceptibility of the specific DNA sites in the control region of minichromosomes to DNAase I decreased in a dose dependent manner after irradiation of isolated nuclei. On the other hand, the irradiation of minichromosomes extracted from nuclei in 0.1 M NaCl-containing buffer almost did not affect the level of their hypersensitivity to DNAase I. This suggests that DNAase I hypersensitivity may be determined by two different mechanisms. One of them may be connected with elastic torsional strain within a fraction of minichromosomes and another seems to be determined by nucleosome free region. The first mechanism may be primarily responsible for the hypersensitivity of minichromosomes within nuclei. After irradiation of the intact cells, DNAase I hypersensitivity tested in nuclei substantially increased. This was connected with activation of endogeneous nucleases by X-irradiation which led to accumulation of single- and double-strand breaks superimposed to DNAase I induced breaks in the control region of SV40 DNA.
研究了X射线照射对细胞核内或溶液中游离的SV40微型染色体的DNA酶I超敏性的影响。分离的细胞核经照射后，微型染色体控制区中特定DNA位点对DNA酶I的敏感性呈剂量依赖性降低。另一方面，在含0.1M NaCl的缓冲液中从细胞核中提取的微型染色体经照射后，几乎不影响其对DNA酶I的超敏水平。这表明DNA酶I超敏性可能由两种不同机制决定。其中一种可能与一部分微型染色体中的弹性扭转应变有关，另一种似乎由无核小体区域决定。第一种机制可能主要负责细胞核内微型染色体的超敏性。完整细胞经照射后，细胞核中检测到的DNA酶I超敏性显著增加。这与X射线照射激活内源性核酸酶有关，导致在SV40 DNA控制区积累单链和双链断裂，叠加在DNA酶I诱导的断裂上。
