Luchnik A N, Glaser V M
Mol Gen Genet. 1981;183(3):553-6. doi: 10.1007/BF00268781.
The topological linking numbers in closed superhelical loops of nuclear DNA were measured as the density of DNA topological turns ('titratable superhelical turns') per unit length of DNA by means of sedimentation of superhelical DNA (in nucleoids) in gradients of 15-30% sucrose containing 1.95 M NaCl and various concentrations of ethidium bromide. In four malignantly transformed Syrian hamster cell lines (three SV40-transformed and one spontaneous) the density of DNA topological turns was equal to or higher than the density of DNA topological turns in early passage embryonal Syrian hamster cells (/delta/ greater than or equal to 0.076) and, in contrast to normal cells, the malignant ones did not decrease the density of their DNA topological turns upon cultivation. It is proposed that the persistence of high densities of DNA topological turns in malignant cells is responsible for activation of transcription of a number of genes during malignant transformation.
通过超螺旋DNA（在类核中）在含有1.95M氯化钠和不同浓度溴化乙锭的15 - 30%蔗糖梯度中的沉降，测量核DNA闭合超螺旋环中的拓扑连接数，以此作为每单位长度DNA的DNA拓扑螺旋密度（“可滴定超螺旋螺旋”）。在四种恶性转化的叙利亚仓鼠细胞系（三种SV40转化的和一种自发转化的）中，DNA拓扑螺旋密度等于或高于早期传代的叙利亚仓鼠胚胎细胞中的DNA拓扑螺旋密度（Δ大于或等于0.076），并且与正常细胞相反，恶性细胞在培养时不会降低其DNA拓扑螺旋密度。有人提出，恶性细胞中高密度DNA拓扑螺旋的持续存在是恶性转化过程中许多基因转录激活的原因。
