UBR7 is a novel chromatin directed E3 ubiquitin ligase

描述(申请人提供)：基因转录由组蛋白的翻译后修饰控制，组蛋白招募基因转录的效应者。组蛋白的翻译后修饰可以导致对基因转录的短期控制，或者它们可以作为基因转录的长期表观遗传决定因素，可以在许多细胞世代之间忠实地传递基因的激活状态。最近的一项大规模外显子筛查发现，在一个自闭症家庭中，UBR7基因发生了突变。UBR7含有一个UBR-box，因此属于一个蛋白质家族，参与识别和泛素化含有N-degron信号序列的蛋白质。UBR7是这七个家族成员中最具差异性的一个，对含有N-降解子的蛋白质没有亲和力。UBR7还包含一个紧邻UBR-box的PhD结构域，这使其有别于其他UBR蛋白。PhD结构域在染色质相关蛋白中很常见，它与翻译后修饰的组蛋白H3氨基末端结合。UBR7的功能和它在自闭症中的作用完全没有定义。我们假设UBR7通过其PhD结构域与染色质结合，并通过组蛋白泛素化来调节转录。与自闭症相关的突变位于UBR-Box和PhD结构域之间。我们预计，与自闭症相关的突变体将改变UBR-box、PHD结构域或两者的功能，并导致导致自闭症发展的基因表达改变。提出的实验包括测试UBR7与修饰组蛋白H3氨基末端的结合，评估UBR7的E3连接酶活性，并确定自闭症相关突变体是否影响这些特性。我们确定了受UBR7调控的基因，并比较了它们在含有野生型和突变型UBR7的细胞中的表达。这些实验将首次从机制上描述一种新的自闭症基因，并表征一种独特的染色质相关蛋白，该蛋白可能会将组蛋白的翻译后修饰与泛素化结合在一起。

DESCRIPTION (provided by applicant): Gene transcription is governed by the posttranslational modification of histones that recruit the effectors of gene transcription. The posttranslational modification of histones can result in short-term control of gene transcription o they can act as long-term epigenetic determinants of gene transcription that can faithfully transmit the activation status of a gene across many cellular generations. A recent large-scale exome screen identified a mutation in the gene UBR7 in a family with autism. UBR7 contains a UBR- box and therefore belongs to a family of proteins involved in the recognition and ubiquitination of proteins that contain an N-degron signal sequence. UBR7 is the most divergent of the seven family members and has no demonstrated affinity for N-degron containing proteins. UBR7 also contains a PHD domain immediately adjacent to the UBR-box which makes it unique from other UBR proteins. PHD domains are common in chromatin associated protein that binds to posttranslationally modified histone H3 amino terminal tails. The function of UBR7 and it role in autism are completely undefined. We hypothesize that UBR7 binds chromatin via its PHD domain and regulates transcription through ubiquitination of histone proteins. The mutation associated with autism lies between the UBR-Box and PHD domains. We expect that the autism-associated mutant will alter the function of the UBR-box, PHD domain or both, and result in altered gene expression that contributes to the development of autism. The experiments proposed with test the binding of UBR7 to modified histone H3 amino terminal tails, assess the E3 ligase activity of UBR7 and determine if the autism associated mutant affects these properties. We determine the genes regulated by UBR7 and compare their expression between cells containing wild-type and mutated UBR7. Together these experiments will provide the first mechanistic description of a new autism gene and characterize a unique chromatin associated protein that may couple posttranslational modification of histones to ubiquitinylation.