Molecular dissection of condensin II-mediated chromosome assembly using in vitro assays

In vertebrates, condensin I and condensin II cooperate to assemble rod-shaped chromosomes during mitosis. Although the mechanism of action and regulation of condensin I have been studied extensively, our corresponding knowledge of condensin II remains very limited. By introducing recombinant condensin II complexes into Xenopus egg extracts, we dissect the roles of its individual subunits in chromosome assembly. We find that one of two HEAT subunits, CAP-D3, plays a crucial role in condensin II-mediated assembly of chromosome axes, whereas the other HEAT subunit, CAP-G2, has a very strong negative impact on this process. The structural maintenance of chromosomes ATPase and the basic amino acid clusters of the kleisin subunit CAP-H2 are essential for this process. Deletion of the C-terminal tail of CAP-D3 increases the ability of condensin II to assemble chromosomes and further exposes a hidden function of CAP-G2 in the lateral compaction of chromosomes. Taken together, our results uncover a multilayered regulatory mechanism unique to condensin II, and provide profound implications for the evolution of condensin II.

Automated summary

In vertebrates, condensin I and condensin II work together to assemble chromosomes during mitosis. However, our understanding of condensin II is limited. Through experiments, we discovered that one of the two HEAT subunits, CAP-D3, plays a crucial role in condensin II-mediated chromosome assembly, while the other HEAT subunit, CAP-G2, has a negative impact on this process. The ATPase protein and basic amino acid clusters of the kleisin subunit CAP-H2 are also essential. Deleting the C-terminal tail of CAP-D3 enhances the ability of condensin II to assemble chromosomes and reveals a hidden function of CAP-G2 in chromosome compaction.