Department of Biochemistry and Biophysics, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, 1450 3(rd) Street, San Francisco, CA 94158, USA.
Curr Biol. 2013 Sep 9;23(17):1638-48. doi: 10.1016/j.cub.2013.06.050. Epub 2013 Aug 22.
In eukaryotes, ribosome biosynthesis involves the coordination of ribosomal RNA and ribosomal protein (RP) production. In S. cerevisiae, the regulation of ribosome biosynthesis occurs largely at the level of transcription. The transcription factor Ifh1 binds at RP genes and promotes their transcription when growth conditions are favorable. Although Ifh1 recruitment to RP genes has been characterized, little is known about the regulation of promoter-bound Ifh1.
We used a novel whole-cell-extract screening approach to identify Spt7, a member of the SAGA transcription complex, and the RP transactivator Ifh1 as highly acetylated nonhistone species. We report that Ifh1 is modified by acetylation specifically in an N-terminal domain. These acetylations require the Gcn5 histone acetyltransferase and are reversed by the sirtuin deacetylases Hst1 and Sir2. Ifh1 acetylation is regulated by rapamycin treatment and stress and limits the ability of Ifh1 to act as a transactivator at RP genes.
Our data suggest a novel mechanism of regulation whereby Gcn5 functions to titrate the activity of Ifh1 following its recruitment to RP promoters to provide more than an all-or-nothing mode of transcriptional regulation. We provide insights into how the action of histone acetylation machineries converges with nutrient-sensing pathways to regulate important aspects of cell growth.
在真核生物中，核糖体生物合成涉及核糖体 RNA 和核糖体蛋白 (RP) 的协调生产。在酿酒酵母中，核糖体生物合成的调节主要发生在转录水平。转录因子 Ifh1 在生长条件有利时结合在 RP 基因上，并促进其转录。虽然已经对 Ifh1 与 RP 基因的募集进行了描述，但对启动子结合的 Ifh1 的调节知之甚少。
我们使用了一种新的全细胞提取物筛选方法来鉴定 Spt7，它是 SAGA 转录复合物的成员，以及 RP 转录激活因子 Ifh1，它们都是高度乙酰化的非组蛋白。我们报告说，Ifh1 在 N 端结构域被乙酰化修饰。这些乙酰化需要 Gcn5 组蛋白乙酰转移酶，并被 sirtuin 去乙酰化酶 Hst1 和 Sir2 逆转。Ifh1 乙酰化受到雷帕霉素处理和应激的调节，限制了 Ifh1 作为 RP 基因转录激活因子的能力。
我们的数据表明了一种新的调节机制，即 Gcn5 在其被募集到 RP 启动子后，通过滴定 Ifh1 的活性来调节其活性，从而提供了一种不仅仅是全有或全无的转录调节模式。我们提供了关于组蛋白乙酰化机器如何与营养感应途径汇聚以调节细胞生长的重要方面的见解。
