Histone H1 compacts DNA under force and during chromatin assembly |
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| Authors: | Botao Xiao Benjamin S. Freedman Kelly E. Miller Rebecca Heald John F. Marko |
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| Affiliation: | University of North Carolina;aDepartment of Physics and Astronomy, Northwestern University, Evanston, IL 60208;dDepartment of Molecular Biosciences, Northwestern University, Evanston, IL 60208;bDepartment of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Boston Children''s Hospital, Boston, MA 02115;cMolecular and Cell Biology Department, University of California, Berkeley, Berkeley, CA 94720 |
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| Abstract: | Histone H1 binds to linker DNA between nucleosomes, but the dynamics and biological ramifications of this interaction remain poorly understood. We performed single-molecule experiments using magnetic tweezers to determine the effects of H1 on naked DNA in buffer or during chromatin assembly in Xenopus egg extracts. In buffer, nanomolar concentrations of H1 induce bending and looping of naked DNA at stretching forces below 0.6 pN, effects that can be reversed with 2.7-pN force or in 200 mM monovalent salt concentrations. Consecutive tens-of-nanometer bending events suggest that H1 binds to naked DNA in buffer at high stoichiometries. In egg extracts, single DNA molecules assemble into nucleosomes and undergo rapid compaction. Histone H1 at endogenous physiological concentrations increases the DNA compaction rate during chromatin assembly under 2-pN force and decreases it during disassembly under 5-pN force. In egg cytoplasm, histone H1 protects sperm nuclei undergoing genome-wide decondensation and chromatin assembly from becoming abnormally stretched or fragmented due to astral microtubule pulling forces. These results reveal functional ramifications of H1 binding to DNA at the single-molecule level and suggest an important physiological role for H1 in compacting DNA under force and during chromatin assembly. |
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