Transcription Through Nucleosomes

在体内，核小体对于RNA聚合酶II(POL II)的转录是“透明的”，但在体外则不是。对POL II的强大体外屏障的性质尚不清楚。核小体在体内转录后仍能存活，但POL II的传递会产生一种“开放”的染色质状态，其中高阶核小体结构会受到干扰。在转录过程中，单个核小体改变了它们在DNA上的位置，一些组蛋白从组蛋白八聚体上解离，组蛋白尾巴被化学修饰。所有这些改变与核小体屏障的强度之间的关系大多是间接的。这是因为缺乏能够分析这一过程的生化细节的体外系统。我们通过设计最小的体外系统来实现这一目标，在该系统中，酵母POL II、POL III和E.Coli RNA聚合酶(RNAP)的核心酶通过定位的单核小体转录。

Nucleosomes are "transparent" to transcription by RNA polymerase II (Pol II) in vivo, but not in vitro. The nature of the strong in vitro barrier to Pol II is unknown. Nucleosomes survive transcription in vivo, but passage of Pol II generates an "open" chromatin state where a high-order nucleosome structure is disturbed. During transcription, the individual nucleosomes change their position on DNA, some histones dissociate from the histone octamer, and the histone tails become chemically modified. The relationship between all these alterations and the strength of the nucleosomal barrier is mostly circumstantial. This is due to the lack of an in vitro system where the biochemical details of the process can be analyzed. We accomplished this goal by designing the "minimal" in vitro system where core enzymes of the yeast Pol II, Pol III, and E. coli RNA polymerase (RNAP) transcribe through a positioned mononucleosome.