Department of Microbiology and Molecular Medicine, University of Geneva, Faculty of Medicine, Geneva, Switzerland.
Mol Cell Biol. 2011 Apr;31(8):1610-23. doi: 10.1128/MCB.01210-10. Epub 2011 Feb 14.
In this study we determine that the Not4 E3 ligase is important for proteasome integrity. Consequently, deletion of Not4 leads to an accumulation of polyubiquitinated proteins and reduced levels of free ubiquitin. In the absence of Not4, the proteasome regulatory particle (RP) and core particle (CP) form salt-resistant complexes, and all other forms of RPs are unstable. Not4 can associate with RP species present in purified proteasome holoenzyme but not with purified RP. Additionally, Not4 interacts with Ecm29, a protein that stabilizes the proteasome. Interestingly, Ecm29 is identified in RP species that are inactive and not detectable in cells lacking Not4. In the absence of Not4, Ecm29 interacts less well with the proteasome and becomes ubiquitinated and degraded. Our results characterize Ecm29 as a proteasome chaperone whose appropriate interaction with the proteasome requires Not4.
在这项研究中，我们确定了 Not4 E3 连接酶对于蛋白酶体的完整性很重要。因此，Not4 的缺失会导致多泛素化蛋白质的积累和游离泛素水平的降低。在没有 Not4 的情况下，蛋白酶体调节颗粒 (RP) 和核心颗粒 (CP) 形成耐盐复合物，并且所有其他形式的 RPs 都不稳定。Not4 可以与存在于纯化的蛋白酶体全酶中的 RP 物种结合，但不能与纯化的 RP 结合。此外，Not4 与 Ecm29 相互作用，Ecm29 是一种稳定蛋白酶体的蛋白质。有趣的是，Ecm29 被鉴定为 RP 物种，其在缺乏 Not4 的细胞中是无活性且不可检测的。在没有 Not4 的情况下，Ecm29 与蛋白酶体的相互作用较差，并且会发生泛素化和降解。我们的结果将 Ecm29 表征为一种蛋白酶体伴侣，其与蛋白酶体的适当相互作用需要 Not4。
