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Proc Natl Acad Sci U S A 2023 Mar 21;12012:e2221309120. doi: 10.1073/pnas.2221309120.
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Monitoring the compaction of single DNA molecules in Xenopus egg extract in real time.

Sun M , Amiri H , Tong AB , Shintomi K , Hirano T , Bustamante C , Heald R .

DNA compaction is required for the condensation and resolution of chromosomes during mitosis, but the relative contribution of individual chromatin factors to this process is poorly understood. We developed a physiological, cell-free system using high-speed Xenopus egg extracts and optical tweezers to investigate real-time mitotic chromatin fiber formation and force-induced disassembly on single DNA molecules. Compared to interphase extract, which compacted DNA by ~60%, metaphase extract reduced DNA length by over 90%, reflecting differences in whole-chromosome morphology under these two conditions. Depletion of the core histone chaperone ASF1, which inhibits nucleosome assembly, decreased the final degree of metaphase fiber compaction by 29%, while depletion of linker histone H1 had a greater effect, reducing total compaction by 40%. Compared to controls, both depletions reduced the rate of compaction, led to more short periods of decompaction, and increased the speed of force-induced fiber disassembly. In contrast, depletion of condensin from metaphase extract strongly inhibited fiber assembly, resulting in transient compaction events that were rapidly reversed under high force. Altogether, these findings support a speculative model in which condensin plays the predominant role in mitotic DNA compaction, while core and linker histones act to reduce slippage during loop extrusion and modulate the degree of DNA compaction.

PubMed ID: 36917660
PMC ID: PMC10041109
Article link: Proc Natl Acad Sci U S A
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: asf1a
GO keywords: mitotic cell cycle [+]

Article Images: [+] show captions
References [+] :
Arimura, Structural features of nucleosomes in interphase and metaphase chromosomes. 2021, Pubmed, Xenbase