Kruithof Maarten, Chien Fan-Tso, Routh Andrew, Logie Colin, Rhodes Daniela, van Noort John
Leiden University, The Netherlands.
Nat Struct Mol Biol. 2009 May;16(5):534-40. doi: 10.1038/nsmb.1590. Epub 2009 Apr 19.
The compaction of eukaryotic DNA into chromatin has been implicated in the regulation of all DNA processes. To unravel the higher-order folding of chromatin, we used magnetic tweezers and probed the mechanical properties of single 197-bp repeat length arrays of 25 nucleosomes. At forces up to 4 pN, the 30-nm fiber stretches like a Hookian spring, resulting in a three-fold extension. Together with a high nucleosome-nucleosome stacking energy, this points to a solenoid as the underlying topology of the 30-nm fiber. Unexpectedly, linker histones do not affect the length or stiffness of the fiber but stabilize its folding. Fibers with a nucleosome repeat length of 167 bp are stiffer, consistent with a two-start helical arrangement. The observed high compliance causes extensive thermal breathing, which forms a physical basis for the balance between DNA condensation and accessibility.
真核生物DNA压缩成染色质与所有DNA过程的调控有关。为了揭示染色质的高级折叠结构，我们使用了磁镊并探测了由25个核小体组成的单个197碱基对重复长度阵列的机械性能。在高达4皮牛的力作用下，30纳米纤维像胡克弹簧一样伸展，产生三倍的伸长。再加上高核小体-核小体堆积能量，这表明螺线管是30纳米纤维的潜在拓扑结构。出乎意料的是，连接组蛋白并不影响纤维的长度或刚度，但能稳定其折叠。核小体重复长度为167碱基对的纤维更硬，这与双起始螺旋排列一致。观察到的高顺应性导致广泛的热呼吸，这为DNA凝聚和可及性之间的平衡形成了物理基础。
