Yarrington Robert M, Rudd Jared S, Stillman David J
Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, Utah, USA.
Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, Utah, USA
Mol Cell Biol. 2015 Feb;35(4):688-98. doi: 10.1128/MCB.01285-14. Epub 2014 Dec 15.
Promoters often contain multiple binding sites for a single factor. The yeast HO gene contains nine highly conserved binding sites for the SCB (Swi4/6-dependent cell cycle box) binding factor (SBF) complex (composed of Swi4 and Swi6) in the 700-bp upstream regulatory sequence 2 (URS2) promoter region. Here, we show that the distal and proximal SBF sites in URS2 function differently. Chromatin immunoprecipitation (ChIP) experiments show that SBF binds preferentially to the left side of URS2 (URS2-L), despite equivalent binding to the left-half and right-half SBF sites in vitro. SBF binding at URS2-L sites depends on prior chromatin remodeling events at the upstream URS1 region. These signals from URS1 influence chromatin changes at URS2 but only at sites within a defined distance. SBF bound at URS2-L, however, is unable to activate transcription but instead facilitates SBF binding to sites in the right half (URS2-R), which are required for transcriptional activation. Factor binding at HO, therefore, follows a temporal cascade, with SBF bound at URS2-L serving to relay a signal from URS1 to the SBF sites in URS2-R that ultimately activate gene expression. Taken together, we describe a novel property of a transcription factor that can have two distinct roles in gene activation, depending on its location within a promoter.
启动子通常包含单个因子的多个结合位点。酵母HO基因在700碱基对的上游调控序列2（URS2）启动子区域含有九个高度保守的SCB（Swi4/6依赖性细胞周期框）结合因子（SBF）复合物（由Swi4和Swi6组成）的结合位点。在这里，我们表明URS2中的远端和近端SBF位点功能不同。染色质免疫沉淀（ChIP）实验表明，尽管SBF在体外与URS2的左半部分和右半部分的SBF位点具有同等结合能力，但它优先结合于URS2的左侧（URS2-L）。URS2-L位点的SBF结合取决于上游URS1区域先前的染色质重塑事件。来自URS1的这些信号影响URS2处的染色质变化，但仅在限定距离内的位点起作用。然而，结合在URS2-L处的SBF无法激活转录，而是促进SBF与右半部分（URS2-R）的位点结合，这些位点是转录激活所必需的。因此，HO处的因子结合遵循时间级联，结合在URS2-L处的SBF用于将来自URS1的信号传递到URS2-R中的SBF位点，最终激活基因表达。综上所述，我们描述了一种转录因子的新特性，即根据其在启动子中的位置，它在基因激活中可以具有两种不同的作用。
