Remodeling and Spacing Factor 1 in Histone H2A Ubiquitination-Mediated Gene Silencing

组蛋白的翻译后修饰在染色质结构的调节中起重要作用， 功能组蛋白H2 A泛素化是一种对多种细胞过程都很重要的主要修饰。 我们以前已经发现，多梳抑制复合物1（PRC 1），一个基本的发展， 调节子，作为H2 AK 119泛素化的泛素连接酶（H2 AK 119 ub）。这项研究将H2 AK 119 ub与 PRC 1介导的关键发育基因的基因沉默和PRC 1在细胞身份中的重要作用， 肿瘤发生和基因组印记。几种蛋白质已被证明可以结合H2 AK 119 ub;然而， 这种修饰导致下游基因沉默事件仍然很不清楚。我们最近发现 重塑和间隔因子1（RSF 1）作为一种新的H2 AK 119 ub结合蛋白，为解剖 H2 AK 119 ub的作用机制。我们发现RSF 1通过先前的一个结合位点与H2 AK 119 ub结合。 未表征的区域指定为泛素化H2 A结合（UAB）基序，RSF 1是必需的， 用于沉默H2 AK 119 ub靶基因和用于维持正常的H2 AK 119 ub核小体模式， 启动子区。我们进一步证明，在非洲爪蟾早期胚胎发育过程中，RSF 1调节 中胚层细胞特化和原肠胚形成的方式类似于环1，非洲爪蟾PRC 1亚基介导 H2AK119ub.尽管这些研究表明RSF 1作为H2 AK 119 ub结合蛋白， H2 AK 119 ub靶基因阻遏，阅读H2 AK 119 ub标记是靶基因阻遏的原因，这一点还有待确定。 RSF 1抑制基因表达的机制。在这里，我们提出了一系列的结构，在体外，并在 描述RSF 1在H2 AK 119 ub功能中的作用机制的体内研究。我们假设RSF 1 是H2 AK 119泛素化的关键阅读器，介导其在基因沉默、染色质 重塑和发展。我们提出解决三个问题的关键这一假设：1）如何 RSF 1特异性识别H2 AK 119 ub核小体？2)RSF 1是如何调节 H2 AK 119 ub染色质？RSF 1在H2 AK 119亚调节的生理性细胞凋亡中的意义 过程？考虑到PRC 1和RSF 1在正常发育过程中细胞命运决定中的基本作用， PRC 1和RSF 1在癌症发展中的广泛参与，这些研究将 这也极大地推进了我们对控制正常发育的表观遗传机制的理解 作为致病过程。

Posttranslational modifications of histones play important roles in the regulation of chromatin structure and function. Histone H2A ubiquitination is a predominant modification important for a variety of cellular processes. We have previously discovered that Polycomb Repressive Complex 1 (PRC1), a fundamental developmental regulator, acts as a ubiquitin ligase for H2AK119 ubiquitination (H2AK119ub). This study links H2AK119ub to PRC1-mediated gene silencing of key developmental genes and the essential roles of PRC1 in cell identity, tumorigenesis, and genomic imprinting. Several proteins have been shown to bind H2AK119ub; however, how this modification elicits downstream gene silencing events remains largely obscure. We recently identified Remodeling and Spacing Factor 1 (RSF1) as a novel H2AK119ub-binding protein, providing a gateway to dissect the mechanism of action of H2AK119ub. We discovered that RSF1 binds H2AK119ub through a previously uncharacterized region designated as the ubiquitinated H2A binding (UAB) motif, and that RSF1 is required both for silencing of H2AK119ub target genes and for maintaining the normal H2AK119ub nucleosome pattern at promoter regions. We further demonstrated that, during Xenopus early embryonic development, RSF1 regulates mesodermal cell specification and gastrulation in a fashion similar to Ring1, a Xenopus PRC1 subunit mediating H2AK119ub. Although these studies reveal that RSF1, as a H2AK119ub-binding protein, is required for H2AK119ub target gene repression, it remains to be established that reading the H2AK119ub mark is the mechanism by which RSF1 represses gene expression. Here, we propose a series of structural, in vitro, and in vivo studies to delineate the mechanism of action of RSF1 in H2AK119ub function. We hypothesize that RSF1 is a key reader of H2AK119 ubiquitination that mediates its roles in gene silencing, chromatin remodeling, and development. We propose to address three questions critical to this hypothesis: 1) how does RSF1 specifically recognize H2AK119ub nucleosomes? 2) how does RSF1 modulate the organization of H2AK119ub chromatin? and 3) what is the significance of RSF1 in H2AK119ub-regulated physiological processes? Given the fundamental roles of PRC1 and RSF1 in cell fate determination during normal development and the extensive involvement of PRC1 and RSF1 in cancer development, these studies will significantly advance our understanding of the epigenetic mechanisms controlling normal development as well as pathogenic processes.