Burch J B, Martinson H G
Nucleic Acids Res. 1980 Nov 11;8(21):4969-87. doi: 10.1093/nar/8.21.4969.
Calf thymus nucleosomes exhibit two different and independent hydrodynamic responses to diminishing salt concentration. One change is gradual over the range 40 to 0.2 mM Na+ and is accompanied by decreases in contact-site cross-linking efficiency. The other change is abrupt, being centered between 1 and 2 mM Na+. We found only one abrupt change in sedimentation rate for particles ranging in DNA content fom 144 to 230 base pairs. This response to decreasing ionic strength is similar for particles of both 169 and 230 base pairs. Core particles (144 base pairs) exhibit a somewhat diminished response. The abrupt change is blocked by formaldehyde or dimethylsuberimidate cross-linking. The blockage by dimethylsuberimidate demonstrates that the abrupt conformational change requires the participation of the core histones. H1 completely blocks the abrupt but not the gradual conformational change. Thus H1 uncouples the different responses to low ionic strength and exerts an important constraint on the conformational states available to the nucleosome core.
小牛胸腺核小体对盐浓度降低呈现出两种不同且独立的流体动力学响应。一种变化在40至0.2 mM Na⁺范围内是渐进的，同时伴随着接触位点交联效率的降低。另一种变化是突然的，集中在1至2 mM Na⁺之间。我们发现，对于DNA含量在144至230个碱基对范围内的颗粒，沉降速率只有一个突然变化。对于169和230个碱基对的颗粒，这种对离子强度降低的响应是相似的。核心颗粒（144个碱基对）的响应有所减弱。这种突然变化被甲醛或亚精胺二甲酯交联所阻断。亚精胺二甲酯的阻断表明，这种突然的构象变化需要核心组蛋白的参与。H1完全阻断了突然的构象变化，但没有阻断渐进的构象变化。因此，H1使对低离子强度的不同响应解偶联，并对核小体核心可利用的构象状态施加了重要限制。
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