Licensing Transcription Activator Activity with Ubiquitin Time Clocks

复杂高等生物的细胞依靠其DNA基因组中包含的信息来提供发育以及如何对环境变化做出反应的指令。细胞基因组中的大部分信息存储在可以通过阅读获得的基因中，从而产生所谓的基因表达。基因表达受许多不同因素的影响而微调，其中激活蛋白起着关键作用。激活剂表现出强大的活性，可以招募所有其他必要的因子来表达他们的目标基因。因此，它们对于获取基因中包含的信息是必不可少的，但同时它们的强大活性也构成了严重的威胁，因为过度的基因表达可能导致基因组的不稳定和突变。因此，未能正确地调节激活剂的活性通常会对生物体造成灾难性的病理后果，包括癌细胞形成、激素失衡、自身免疫或免疫功能低下。尽管激活剂功能障碍会带来严重的惩罚，但人们对细胞如何调节自己的活动知之甚少。最近，来自我们实验室和其他实验室的数据显示，许多有效的激活剂是不稳定的蛋白质，因为它们与小蛋白泛素的链融合在一起，泛素是激活剂降解的信号。根据这些数据，已经假设细胞为激活剂提供了有限的活动许可证，当该许可证到期时，激活剂被降级。虽然这是一种有吸引力的机制来控制激活剂，但这一许可证的分子身份及其有效期仍然难以捉摸。我们最新的基因实验表明，我们现在能够通过突变酶来捕获处于完全许可状态的激活剂，这些酶可能会改变融合到激活剂上的泛素链的长度。在这里，我们将详细研究这些酶，因为它们指出泛素链长是激活活性的可调时间时钟。使用遗传、基因组和生化工具，我们将识别参与这一过程的所有泛素链修饰酶，并评估它们在许可激活剂活性方面的作用。揭开激活剂活性微调的机制，将为从人类到植物的高等生物如何监管其基因组中包含的信息的获取提供深刻的洞察。这些基本知识为设计治疗一系列人类疾病的新药或疗法以及以新的作物保护战略实现农业现代化奠定了基础。

Cells of complex higher organisms rely on information contained in their DNA genomes to provide instructions for development and how to respond to changes in their environment. The majority of information in the cell's genome is stored in genes that can be accessed by reading them, resulting in so-called gene expression. Gene expression is fine-tuned by the action of many different factors, amongst which activator proteins play a pivotal role. Activators exhibit potent activity that recruits all the other necessary factors for the expression of their target genes. They are therefore indispensable for accessing the information contained in genes but at the same time their strong activity poses a serious threat, as excessive gene expression can lead to genome instability and mutation. Accordingly, failure to correctly regulate the activity of activators often has catastrophic pathological consequences for an organism, including cancer cell formation, hormone imbalance, and either autoimmunity or low immune function. Despite the serious penalties associated with activator dysfunction, little is understood about how cells regulate their activity. Recently, data from our lab and others showed that many potent activators are unstable proteins because they are fused with chains of the small protein ubiquitin, a signal for activator degradation. From these data it has been hypothesized that cells provide activators with a limited license for activity and when this license expires the activator is degraded. While this is an attractive mechanism for keeping activators in check, the molecular identity of this license and the length of its validity remain elusive. Our latest genetic experiments suggest that we are now able to trap activators in their fully licensed states by mutating enzymes that potentially modify the length of ubiquitin chains fused to activators. Here we will investigate these enzymes in detail as they point to ubiquitin chain length being an adjustable time clock for activator activity. Using genetic, genomic, and biochemical tools we will identify all ubiquitin chain modifying enzymes involved in this process and assess their role in licensing activator activity. Unravelling the mechanisms by which activator activity is fine-tuned will provide deep insight into how higher organisms -from humans to plants- regulate access to information contained within their genomes. Such fundamental knowledge offers the foundation for designing new medicines or therapies to tackle a range of human diseases and for modernizing agriculture with novel crop protection strategies.