Abstract
Imp9 is the primary importin for shuttling H2A-H2B from the cytoplasm to the nucleus. It employs an unusual mechanism where the binding of RanGTP is insufficient to release H2A-H2B. The resulting stable RanGTP·Imp9·H2A-H2B complex gains nucleosome assembly activity with H2A-H2B able to be deposited into an assembling nucleosome in vitro. Using hydrogen-deuterium exchange coupled with mass spectrometry (HDX), we show that Imp9 stabilizes H2A-H2B beyond the direct-binding site, like other histone chaperones. HDX also shows that binding of RanGTP releases H2A-H2B contacts at Imp9 HEAT repeats 4–5, but not 18–19. DNA- and histone-binding surfaces of H2A-H2B are exposed in the ternary complex, facilitating nucleosome assembly. We also reveal that RanGTP has a weaker affinity for Imp9 when H2A-H2B is bound. Imp9 thus provides a connection between the nuclear import of H2A-H2B and its deposition into chromatin.
Original language | English (US) |
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Pages (from-to) | 903-911.e3 |
Journal | Structure |
Volume | 31 |
Issue number | 8 |
DOIs | |
State | Published - Aug 3 2023 |
Keywords
- HDX
- Importin-9
- Ran GTPase
- histones
- importin
- mass spectrometry
- nuclear import
- nucleosome
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology