Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63108, USA.
Curr Biol. 2011 Oct 11;21(19):1624-34. doi: 10.1016/j.cub.2011.08.036. Epub 2011 Sep 29.
The cohesin complex mediates sister chromatid cohesion and regulates gene transcription. Prior studies show that cohesin preferentially binds and regulates genes that control growth and differentiation and that even mild disruption of cohesin function alters development. Here we investigate how cohesin specifically recognizes and regulates genes that control development in Drosophila.
Genome-wide analyses show that cohesin selectively binds genes in which RNA polymerase II (Pol II) pauses just downstream of the transcription start site. These genes often have GAGA factor (GAF) binding sites 100 base pairs (bp) upstream of the start site, and GT dinucleotide repeats 50 to 800 bp downstream in the plus strand. They have low levels of histone H3 lysine 36 trimethylation (H3K36me3) associated with transcriptional elongation, even when highly transcribed. Cohesin depletion does not reduce polymerase pausing, in contrast to depletion of the NELF (negative elongation factor) pausing complex. Cohesin, NELF, and Spt5 pausing and elongation factor knockdown experiments indicate that cohesin does not inhibit binding of polymerase to promoters or physically block transcriptional elongation, but at genes that it strongly represses, it hinders transition of paused polymerase to elongation at a step distinct from those controlled by Spt5 and NELF.
Our findings argue that cohesin and pausing factors are recruited independently to the same genes, perhaps by GAF and the GT repeats, and that their combined action determines the level of actively elongating RNA polymerase.
黏合蛋白复合物介导姐妹染色单体黏合,并调控基因转录。先前的研究表明,黏合蛋白优先结合并调控控制生长和分化的基因,即使是轻微的黏合蛋白功能障碍也会改变发育。在这里,我们研究了黏合蛋白如何特异性识别和调控控制果蝇发育的基因。
全基因组分析表明,黏合蛋白选择性地结合 RNA 聚合酶 II(Pol II)在转录起始位点下游刚刚暂停的基因。这些基因通常在起始位点上游 100 个碱基对(bp)处有 GAGA 因子(GAF)结合位点,在正链上 50 到 800 bp 处有 GT 二核苷酸重复。即使转录水平很高,它们也具有与转录延伸相关的低水平组蛋白 H3 赖氨酸 36 三甲基化(H3K36me3)。黏合蛋白耗竭不会减少聚合酶暂停,与 NELF(负延伸因子)暂停复合物的耗竭相反。黏合蛋白、NELF 和 Spt5 暂停和延伸因子敲低实验表明,黏合蛋白不会抑制聚合酶与启动子的结合,也不会物理阻断转录延伸,但在它强烈抑制的基因上,它会阻碍暂停聚合酶向延伸的转变,这与 Spt5 和 NELF 控制的步骤不同。
我们的研究结果表明,黏合蛋白和暂停因子可能通过 GAF 和 GT 重复序列独立地被招募到相同的基因上,它们的共同作用决定了活跃延伸的 RNA 聚合酶的水平。