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XB-ART-56818
Elife January 1, 2019; 8

Importin-9 wraps around the H2A-H2B core to act as nuclear importer and histone chaperone.

Padavannil A , Sarkar P , Kim SJ , Cagatay T , Jiou J , Brautigam CA , Tomchick DR , Sali A , D'Arcy S , Chook YM .


Abstract
We report the crystal structure of nuclear import receptor Importin-9 bound to its cargo, the histones H2A-H2B. Importin-9 wraps around the core, globular region of H2A-H2B to form an extensive interface. The nature of this interface coupled with quantitative analysis of deletion mutants of H2A-H2B suggests that the NLS-like sequences in the H2A-H2B tails play a minor role in import. Importin-9•H2A-H2B is reminiscent of interactions between histones and histone chaperones in that it precludes H2A-H2B interactions with DNA and H3-H4 as seen in the nucleosome. Like many histone chaperones, which prevent inappropriate non-nucleosomal interactions, Importin-9 also sequesters H2A-H2B from DNA. Importin-9 appears to act as a storage chaperone for H2A-H2B while escorting it to the nucleus. Surprisingly, RanGTP does not dissociate Importin-9•H2A-H2B but assembles into a RanGTP•Importin-9•H2A-H2B complex. The presence of Ran in the complex, however, modulates Imp9-H2A-H2B interactions to facilitate its dissociation by DNA and assembly into a nucleosome.

PubMed ID: 30855230
PMC ID: PMC6453568
Article link: Elife
Grant support: [+]

Species referenced: Xenopus
Genes referenced: h2ac21 h2bc21 mbp napsa pcna ran tab3


Article Images: [+] show captions
References [+] :
Adams, Chromatin assembly: biochemical identities and genetic redundancy. 1999, Pubmed