Condensin association with chromosomes depends on a DNA binding domain formed by its HEAT-repeat subunits

Condensin protein complexes play central roles in the three-dimensional organization of chromosomes during mitotic and meiotic cell divisions. How condensin interacts with its chromatin substrates to promote sister chromatid decatenation and segregation is largely unknown. Previous work suggested that condensin, in addition to encircling chromatin fibers topologically within the large ring-shaped structure formed by its structural maintenance of chromosomes (SMC) and kleisin subunits, contacts DNA directly. Here we describe the discovery of a binding domain for double-stranded DNA helices formed by condensin’s HEAT-repeat subunits. Using detailed mapping data of the interfaces between the HEAT-repeat and the kleisin subunits, we generated mutant complexes that lack the Ycg1/CAP-G HEAT-repeat subunit. These tetrameric condensin complexes fail to associate stably with chromosomes in yeast and human cells. We suggest that condensin controls chromosome architecture by stabilizing chromatin loops of chromatin fibers through interaction with its unconventional HEAT-repeat DNA binding domain. Overall design: Analysis of condensin binding genomewide in a wild type and a condensin mutant

凝缩蛋白（Condensin）复合物在有丝分裂与减数分裂的细胞分裂过程中，对染色体的三维组织发挥核心作用。目前学界对凝缩蛋白如何与其染色质底物相互作用，以促进姐妹染色单体的解连环与分离仍知之甚少。此前研究表明，凝缩蛋白除通过其染色体结构维持（SMC）与克莱辛（kleisin）亚基形成的大型环状结构，以拓扑方式环绕染色质纤维外，还可直接与DNA结合。本研究首次揭示了由凝缩蛋白的HEAT重复（HEAT-repeat）亚基构成的双链DNA螺旋结合结构域。研究人员借助HEAT重复亚基与克莱辛亚基之间相互作用界面的精细定位数据，构建了缺失Ycg1/CAP-G HEAT重复亚基的突变复合物。实验结果显示，这类四聚体凝缩蛋白复合物无法在酵母与人类细胞中与染色体形成稳定结合。我们提出，凝缩蛋白可通过其非典型HEAT重复DNA结合结构域与染色质纤维相互作用，进而稳定染色质环，以此调控染色体的三维构象。实验整体设计：在野生型细胞与凝缩蛋白突变体细胞中开展全基因组范围的凝缩蛋白结合分析。