Gale J M, Smerdon M J
Biochemistry/Biophysics Program, Washington State University, Pullman 99164-4660.
Biochemistry. 1988 Sep 20;27(19):7197-205. doi: 10.1021/bi00419a006.
We have examined the ability of intact and histone H1 depleted chromatin fibers to fold into higher ordered structures in vitro following DNA damage by two different agents: UV irradiation at 254 nm and trimethylpsoralen plus near-UV light. Both agents damage DNA specifically, yet cause different degrees of unwinding (and possibly bending) of the DNA helix. In addition, trimethylpsoralen forms interstrand DNA cross-links. The structural transitions of intact and histone H1 depleted chromatin fibers, induced by NaCl, were monitored by analytical ultracentrifugation, light scattering, and circular dichroism. Our results indicate that when chromatin fibers contain even large, nonphysiological amounts of DNA photodamage by either agent, the salt-induced folding of these fibers into higher ordered structures is unaffected. The compact 30-nm fiber must therefore be able to accommodate a large amount of DNA photodamage (greater than one UV-induced photoproduct or trimethylpsoralen interstrand cross-link per nucleosome) with little or no change in the overall size or compaction of this structure.
我们研究了完整的和组蛋白H1缺失的染色质纤维在受到两种不同试剂造成的DNA损伤后，于体外折叠成更高有序结构的能力：254nm紫外线照射以及三甲基补骨脂素加近紫外线。这两种试剂均特异性损伤DNA，但会导致DNA螺旋不同程度的解旋（以及可能的弯曲）。此外，三甲基补骨脂素会形成链间DNA交联。通过分析超速离心、光散射和圆二色性监测由NaCl诱导的完整的和组蛋白H1缺失的染色质纤维的结构转变。我们的结果表明，当染色质纤维包含即使大量由任一试剂造成的非生理性DNA光损伤时，盐诱导这些纤维折叠成更高有序结构不受影响。因此，紧密的30nm纤维必定能够容纳大量DNA光损伤（每个核小体大于一个紫外线诱导的光产物或三甲基补骨脂素链间交联），而该结构的整体大小或压缩几乎没有变化。
