Institut Curie, PSL University, Sorbonne Université, CNRS, Nuclear Dynamics, 75005 Paris, France.
Institut Pasteur, Unité Régulation Spatiale des Génomes, CNRS, UMR 3525, C3BI USR 3756, F-75015 Paris, France.
Genome Res. 2021 Mar;31(3):411-425. doi: 10.1101/gr.267872.120. Epub 2021 Feb 12.
Physical contacts between distant loci contribute to regulate genome function. However, the molecular mechanisms responsible for settling and maintaining such interactions remain poorly understood. Here, we investigate the well-conserved interactions between heterochromatin loci. In budding yeast, the 32 telomeres cluster in 3-5 foci in exponentially growing cells. This clustering is functionally linked to the formation of heterochromatin in subtelomeric regions through the recruitment of the silencing SIR complex composed of Sir2/3/4. Combining microscopy and Hi-C on strains expressing different alleles of , we show that the binding of Sir3 directly promotes long-range contacts between distant regions, including the rDNA, telomeres, and internal Sir3-bound sites. Furthermore, we unveil a new property of Sir3 in promoting rDNA compaction. Finally, using a synthetic approach, we demonstrate that Sir3 can bond loci belonging to different chromosomes together, when targeted to these loci, independently of its interaction with its known partners (Rap1, Sir4), Sir2 activity, or chromosome context. Altogether, these data suggest that Sir3 acts as a molecular bridge that stabilizes long-range interactions.
物理接触在远距离基因座之间有助于调节基因组功能。然而，负责确定和维持这种相互作用的分子机制仍知之甚少。在这里，我们研究了异染色质基因座之间的高度保守相互作用。在芽殖酵母中，32 个端粒在指数生长细胞中聚集在 3-5 个焦点中。这种聚集通过沉默 SIR 复合物的募集与着丝粒区域中的异染色质形成在功能上相关，该复合物由 Sir2/3/4 组成。在表达不同 等位基因的菌株上结合显微镜和 Hi-C，我们表明 Sir3 的结合直接促进了包括 rDNA、端粒和内部 Sir3 结合位点在内的远距离区域之间的长距离接触。此外，我们揭示了 Sir3 在促进 rDNA 紧缩方面的一个新特性。最后，通过合成方法，我们证明了当靶向这些基因座时，Sir3 可以将属于不同染色体的基因座结合在一起，而不依赖于其与已知伴侣（Rap1、Sir4）、Sir2 活性或染色体背景的相互作用。总而言之，这些数据表明 Sir3 作为一种分子桥，稳定长距离相互作用。
