Williams Stephanie K, Tyler Jessica K
Department of Biochemistry and Molecular Genetics, University of Colorado at Denver and Health Sciences Center, Aurora, CO 80045, USA.
Curr Opin Genet Dev. 2007 Apr;17(2):88-93. doi: 10.1016/j.gde.2007.02.001. Epub 2007 Feb 20.
The packaging of the eukaryotic genome into chromatin severely restricts the access of the transcriptional machinery to the DNA. Recent studies reveal that histones are removed and replaced to enable or restrict, respectively, access of the transcription machinery to regulate transcription. Chromatin disassembly at promoters enables transcriptional activation, whereas promoter chromatin reassembly represses transcription. Histone loss also occurs within transcription units to enable passage of the RNA polymerase, but in this case the histones are rapidly replaced, sometimes by 'variant' histones with specific properties that might serve as a memory of transcriptional competence. Furthermore, the ultimate goal of some epigenetic modifications might well turn out to be the regulation of histone occupancy on the DNA.
真核生物基因组包装成染色质会严重限制转录机制与DNA的接触。最近的研究表明，组蛋白会被去除并替换，分别以允许或限制转录机制的接触来调节转录。启动子处的染色质解聚可实现转录激活，而启动子染色质重新组装则会抑制转录。转录单元内也会发生组蛋白丢失，以使RNA聚合酶能够通过，但在这种情况下，组蛋白会迅速被替换，有时会被具有特定特性的“变体”组蛋白替换，这些特性可能作为转录能力的一种记忆。此外，一些表观遗传修饰的最终目标很可能是调节组蛋白在DNA上的占有率。
