Chromatin Structure Is Implicated in "Late" Elongation Checkpoints on the U2 snRNA and β-Actin Genes
Chromatin Structure Is Implicated in "Late" Elongation Checkpoints on the U2 snRNA and β-Actin Genes
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DOI：
10.1128/mcb.00189-09
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发表时间：
2009-07-01
影响因子：
5.3
通讯作者：
Murphy, Shona
中科院分区：
文献类型：
--
作者：
Egloff, Sylvain;Al-Rawaf, Hadeel;Murphy, Shona
负延伸因子 NELF 是早期延伸检查点的关键组成部分，通常位于蛋白质编码基因转录起始位点的 100 bp 范围内。该检查点的协商以及向生产性延伸的转化需要通过正转录延伸因子 b (P-TEFb) 对 RNA 聚合酶 II (pol II)、NELF 和 DRB 敏感性诱导因子 (DSIF) 的羧基末端结构域进行磷酸化。 P-TEFb 对于非编码 U2 snRNA 基因的转录是可有可无的，这表明 NELF 依赖性检查点不存在。然而，我们发现 800 bp U2 基因转录单元末端的 NELF 和 RNA 干扰介导的 NELF 敲低会导致终止缺陷。 NELF 还与 β-肌动蛋白基因转录起始位点下游 800 bp 相关，此处出现“晚期”P-TEFb 依赖性检查点。有趣的是，这两个基因都有一个延伸的核小体耗尽区域，直至 NELF 依赖性控制点。在这两种情况下，通过该区域的转录均不依赖于 P-TEFb，这表明染色质参与了终止子/检查点的形成。此外，CTCF 与 NELF 在 U2 和 β-肌动蛋白基因上共定位，这增加了它有助于这些基因上 NELF 依赖性控制点的定位和/或功能的可能性。
The negative elongation factor NELF is a key component of an early elongation checkpoint generally located within 100 bp of the transcription start site of protein-coding genes. Negotiation of this checkpoint and conversion to productive elongation require phosphorylation of the carboxy-terminal domain of RNA polymerase II (pol II), NELF, and DRB sensitivity-inducing factor (DSIF) by positive transcription elongation factor b (P-TEFb). P-TEFb is dispensable for transcription of the noncoding U2 snRNA genes, suggesting that a NELF-dependent checkpoint is absent. However, we find that NELF at the end of the 800-bp U2 gene transcription unit and RNA interference-mediated knockdown of NELF causes a termination defect. NELF is also associated 800 bp downstream of the transcription start site of the beta-actin gene, where a "late" P-TEFb-dependent checkpoint occurs. Interestingly, both genes have an extended nucleosome-depleted region up to the NELF-dependent control point. In both cases, transcription through this region is P- TEFb independent, implicating chromatin in the formation of the terminator/checkpoint. Furthermore, CTCF colocalizes with NELF on the U2 and beta-actin genes, raising the possibility that it helps the positioning and/or function of the NELF-dependent control point on these genes.