Endoh Takashi, Iyaguchi Daisuke, Sasaki Naoki, Tanaka Isao, Nakata Mitsuo
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan.
Biopolymers. 2003 Apr;68(4):486-96. doi: 10.1002/bip.10346.
Interaction of DNA-binding protein HU from Bacillus stearothermophilis (HUBst) with coliphage T2 DNA was investigated by observing an elongational flow-induced birefringence, Deltan, of a T2-phage DNA aqueous solution at various HU concentrations. Localized flow birefringence was observed in the pure elongational flow region, and the strain rate dependence of Deltan had a critical strain rate epsilon;(c) for the appearance of flow birefringence at all of the HU concentrations examined, indicating that a coil-stretch transition occurred at epsilon;(c) in each DNA-HU system. For strain rates larger than epsilon;(c), Deltan increased rapidly and then gradually, approaching a plateau value. The value of epsilon;(c) increased with an increase in HU concentration. Analysis based on the relationship between epsilon; (c) and the Rouse-Zimm relaxation time revealed that the increase in epsilon;(c)with increase in HU can be explained by the decrease in the size of the DNA-HU complex. The plateau birefringence value, Deltan(p), decreased at small HU concentrations but did not change at larger HU concentrations. Considering that Deltan(p) is related to the orientational order parameter of segments, it was concluded that there were at least two stages in the process of compaction of DNA induced by HU.
通过观察嗜热脂肪芽孢杆菌（HUBst）的DNA结合蛋白HU与大肠杆菌噬菌体T2 DNA在不同HU浓度下的拉伸流动诱导双折射（Δn），研究了它们之间的相互作用。在纯拉伸流动区域观察到局部流动双折射，并且在所有检测的HU浓度下，Δn的应变率依赖性都有一个临界应变率ε(c)，用于流动双折射的出现，这表明在每个DNA-HU系统中，在ε(c)处发生了线圈-拉伸转变。对于大于ε(c)的应变率，Δn迅速增加，然后逐渐增加，接近一个平台值。ε(c)的值随着HU浓度的增加而增加。基于ε(c)与Rouse-Zimm松弛时间之间的关系进行分析表明，随着HU增加，ε(c)的增加可以通过DNA-HU复合物尺寸的减小来解释。平台双折射值Δn(p)在低HU浓度下降低，但在高HU浓度下没有变化。考虑到Δn(p)与链段的取向序参数有关，得出结论，HU诱导的DNA压缩过程至少有两个阶段。
