Sasi R, Hüvös P E, Fasman G D
J Biol Chem. 1982 Oct 10;257(19):11448-54.
The nature of the binding of a high mobility group protein (HMG 17) to native and H1-H5-depleted chicken erythrocyte chromatin was studied, as a function of ionic strength, using circular dichroism and thermal denaturation techniques. The circular dichroism properties of the HMG 17-reconstituted whole chromatin and H1-H5-depleted chromatin demonstrated that a condensation of chromatin structure occurred upon HMG 17 binding at low ionic strength (1 mM Na phosphate, 0.25 mM EDTA, pH 7.0). Thermal denaturation profiles confirmed this change in the structure of chromatin induced by HMG 17. Thermal denaturation profiles were resolved into three-component transitions. In general, a shift in the temperature of maximum dh/dT for each transition (Tm) was observed for all transitions upon HMG 17 binding. DNA melting in the first transition, originating from linker regions of whole chromatin, was nearly totally depleted and was distributed mainly into the highest melting transition. The same trends were also observed in H1-H5-depleted chromatin. These results indicate that the binding sites of HMG 17 are situated in the linker regions immediately adjacent to the core. The nature of the interaction of HMG 17 at higher ionic strength (50 mM NaCl, 1 mM Na phosphate, 0.25 mM EDTA, pH 7.0) with whole chromatin and H1-H5-depleted chromatin was found to be different but a decrease in [theta] values was found in both chromatins. These observations suggest that HMG 17 does not loosen chromatin structure but produces an overall stabilization and condensation of structure. The implications of these results to the currently accepted models of transcriptionally active chromatin are discussed.
利用圆二色性和热变性技术，研究了高迁移率族蛋白（HMG 17）与天然及去除H1 - H5的鸡红细胞染色质结合的性质，该性质是离子强度的函数。HMG 17重组的完整染色质和去除H1 - H5的染色质的圆二色性特性表明，在低离子强度（1 mM磷酸钠，0.25 mM EDTA，pH 7.0）下HMG 17结合时发生了染色质结构的凝聚。热变性曲线证实了HMG 17诱导的染色质结构变化。热变性曲线被解析为三组分转变。一般来说，在HMG 17结合后，所有转变的最大dh/dT温度（Tm）都发生了变化。第一个转变中源于完整染色质连接区的DNA解链几乎完全消失，并主要分布到最高解链转变中。在去除H1 - H5的染色质中也观察到了相同的趋势。这些结果表明，HMG 17的结合位点位于紧邻核心的连接区。发现HMG 17在较高离子强度（50 mM NaCl，1 mM磷酸钠，0.25 mM EDTA，pH 7.0）下与完整染色质和去除H1 - H5的染色质的相互作用性质不同，但两种染色质中的[θ]值均降低。这些观察结果表明，HMG 17不会使染色质结构松散，而是产生整体的结构稳定和凝聚。讨论了这些结果对当前公认的转录活性染色质模型的影响。
