Selleck William, Fortin Israël, Sermwittayawong Decha, Côté Jacques, Tan Song
Center for Gene Regulation, Department of Biochemistry & Molecular Biology, 108 Althouse Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-1014, USA.
Mol Cell Biol. 2005 Jul;25(13):5535-42. doi: 10.1128/MCB.25.13.5535-5542.2005.
Chromatin modification complexes are key gene regulatory factors which posttranslationally modify the histone component of chromatin with epigenetic marks. To address what features of chromatin modification complexes are responsible for the specific recognition of nucleosomes compared to naked histones, we have performed a functional dissection of the Esa1-containing Saccharomyces cerevisiae Piccolo NuA4 histone acetyltransferase complex. Our studies define the Piccolo determinants sufficient to assemble its three subunits into a complex as well as Piccolo determinants sufficient to specifically acetylate a chromatin template. We find that the conserved Enhancer of Polycomb A (EPcA) homology region of the Epl1 component and the N-terminal 165 amino acids of the Yng2 component of Piccolo are sufficient with Esa1 to specifically act on nucleosomes. We also find that the Esa1 chromodomain plays a critical role in Piccolo's ability to distinguish between histones and nucleosomes. In particular, specific point mutations in the chromodomain putative hydrophobic cage which strongly hinder growth in yeast greatly reduce histone acetyltransferase activity on nucleosome substrates, independent of histone methylation or other modifications. However, the chromodomain is not required for Piccolo to bind to nucleosomes, suggesting a role for the chromodomain in a catalysis step after nucleosome binding.
染色质修饰复合物是关键的基因调控因子，它们通过表观遗传标记对染色质的组蛋白成分进行翻译后修饰。为了探究与裸组蛋白相比，染色质修饰复合物的哪些特征负责对核小体的特异性识别，我们对含有Esa1的酿酒酵母小型NuA4组蛋白乙酰转移酶复合物进行了功能剖析。我们的研究确定了足以将其三个亚基组装成复合物的小型决定因素，以及足以特异性乙酰化染色质模板的小型决定因素。我们发现，Epl1组分的保守多梳增强子A（EPcA）同源区域和小型Yng2组分的N端165个氨基酸与Esa1一起足以特异性作用于核小体。我们还发现，Esa1染色质结构域在小型区分组蛋白和核小体的能力中起关键作用。特别是，染色质结构域假定疏水笼中的特定点突变严重阻碍酵母生长，大大降低了对核小体底物的组蛋白乙酰转移酶活性，与组蛋白甲基化或其他修饰无关。然而，染色质结构域对于小型结合核小体不是必需的，这表明染色质结构域在核小体结合后的催化步骤中起作用。
