Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, Unité Propre de Recherche, Conventionné avec l'Université de Strasbourg, Strasbourg, France.
EMBO J. 2011 Feb 16;30(4):731-43. doi: 10.1038/emboj.2010.359. Epub 2011 Jan 14.
Protein ubiquitylation regulates a broad variety of biological processes in all eukaryotes. Recent work identified a novel class of cullin-containing ubiquitin ligases (E3s) composed of CUL4, DDB1, and one WD40 protein, believed to act as a substrate receptor. Strikingly, CUL4-based E3 ligases (CRL4s) have important functions at the chromatin level, including responses to DNA damage in metazoans and plants and, in fission yeast, in heterochromatin silencing. Among putative CRL4 receptors we identified MULTICOPY SUPPRESSOR OF IRA1 (MSI1), which belongs to an evolutionary conserved protein family. MSI1-like proteins contribute to different protein complexes, including the epigenetic regulatory Polycomb repressive complex 2 (PRC2). Here, we provide evidence that Arabidopsis MSI1 physically interacts with DDB1A and is part of a multimeric protein complex including CUL4. CUL4 and DDB1 loss-of-function lead to embryo lethality. Interestingly, as in fis class mutants, cul4 mutants exhibit autonomous endosperm initiation and loss of parental imprinting of MEDEA, a target gene of the Arabidopsis PRC2 complex. In addition, after pollination both MEDEA transcript and protein accumulate in a cul4 mutant background. Overall, our work provides the first evidence of a physical and functional link between a CRL4 E3 ligase and a PRC2 complex, thus indicating a novel role of ubiquitylation in the repression of gene expression.
蛋白质泛素化调节所有真核生物中广泛的生物过程。最近的工作鉴定了一类新型的含有 CUL4、DDB1 和一个 WD40 蛋白的 cullin 包含的泛素连接酶 (E3)，它们被认为作为底物受体起作用。引人注目的是，基于 CUL4 的 E3 连接酶 (CRL4) 在染色质水平上具有重要功能，包括在后生动物和植物中对 DNA 损伤的反应，以及在裂殖酵母中对异染色质沉默的反应。在推定的 CRL4 受体中，我们鉴定了 MULTICOPY SUPPRESSOR OF IRA1 (MSI1)，它属于进化上保守的蛋白质家族。MSI1 样蛋白有助于不同的蛋白质复合物，包括表观遗传调节 Polycomb 抑制复合物 2 (PRC2)。在这里，我们提供的证据表明拟南芥 MSI1 与 DDB1A 物理相互作用，是包括 CUL4 在内的多聚体蛋白复合物的一部分。CUL4 和 DDB1 的功能丧失导致胚胎致死。有趣的是，与 fis 类突变体一样，cul4 突变体表现出自发的胚乳起始和 MEDEA 的亲本印迹丢失，MEDEA 是拟南芥 PRC2 复合物的靶基因。此外，授粉后，MEDEA 转录本和蛋白质在 cul4 突变体背景中积累。总体而言，我们的工作首次提供了 CRL4 E3 连接酶和 PRC2 复合物之间物理和功能联系的证据，从而表明泛素化在基因表达抑制中的新作用。
