Hovatter K R, Martinson H G
Proc Natl Acad Sci U S A. 1987 Mar;84(5):1162-6. doi: 10.1073/pnas.84.5.1162.
Several polynucleotides that assume an A-form helical structure in solution are unable to form nucleosomes. We attempted to establish a relationship between the ease of the A-form----B-form helix transition and ease of nucleosome formation by reconstituting nucleosomes using ribosubstituted DNA containing various levels of ribonucleotides. Instead we discovered that, when riboadenosine is substituted for deoxyriboadenosine, even one ribonucleotide per 125 base pairs of DNA reduces nucleosome formation and that DNA containing greater than 5% ribonucleotide is completely unable to form nucleosomes. Ribosubstituted DNA restriction fragments exhibited altered mobility on native 6% polyacrylamide gels, indicating an altered helical structure (probably bending). The effects on both nucleosome formation and gel mobility are nucleotide specific and are correlated, being greatest for riboadenosine and decreasing in the order riboadenosine greater than riboguanosine greater than ribocytosine. The results are consistent with the hypothesis that the rate of nucleosome formation can be drastically reduced by isolated local perturbations, such as kinking or bending, in the helical structure of DNA.
几种在溶液中呈现A-型螺旋结构的多核苷酸无法形成核小体。我们试图通过使用含有不同核糖核苷酸水平的核糖取代DNA重建核小体，来建立A-型向B-型螺旋转变的难易程度与核小体形成的难易程度之间的关系。相反，我们发现，当核糖腺苷取代脱氧核糖腺苷时，即使每125个碱基对的DNA中有一个核糖核苷酸，也会减少核小体的形成，并且核糖核苷酸含量大于5%的DNA完全无法形成核小体。核糖取代的DNA限制性片段在天然6%聚丙烯酰胺凝胶上显示出改变的迁移率，表明螺旋结构发生了改变（可能是弯曲）。对核小体形成和凝胶迁移率的影响具有核苷酸特异性且相互关联，对核糖腺苷的影响最大，按核糖腺苷大于核糖鸟苷大于核糖胞苷的顺序递减。这些结果与以下假设一致，即核小体形成的速率可以通过DNA螺旋结构中孤立的局部扰动（如扭结或弯曲）而大幅降低。
