DAXX envelops an H3.3-H4 dimer for H3.3-specific recognition

1] Laboratory of Chromatin Biology and Epigenetics, The Rockefeller University, New York, New York 10065, USA [2] MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK [3].
Nature (Impact Factor: 41.46). 10/2012; 491(7425). DOI: 10.1038/nature11608
Source: PubMed


Histone chaperones represent a structurally and functionally diverse family of histone-binding proteins that prevent promiscuous interactions of histones before their assembly into chromatin. DAXX is a metazoan histone chaperone specific to the evolutionarily conserved histone variant H3.3. Here we report the crystal structures of the DAXX histone-binding domain with a histone H3.3-H4 dimer, including mutants within DAXX and H3.3, together with in vitro and in vivo functional studies that elucidate the principles underlying H3.3 recognition specificity. Occupying 40% of the histone surface-accessible area, DAXX wraps around the H3.3-H4 dimer, with complex formation accompanied by structural transitions in the H3.3-H4 histone fold. DAXX uses an extended α-helical conformation to compete with major inter-histone, DNA and ASF1 interaction sites. Our structural studies identify recognition elements that read out H3.3-specific residues, and functional studies address the contributions of Gly 90 in H3.3 and Glu 225 in DAXX to chaperone-mediated H3.3 variant recognition specificity.

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    • "Although this similarity suggests that HIRA is important in zygote chromatin dynamics in Arabidopsis, null alleles of hira, ubn1, ubn2 and cabin1 and their combinations are fertile and do not show defects in fertilization or early embryogenesis. This lack of impact of HIRA is likely explained by redundancy originating either from another H3.3 incorporation pathway depending on Arabidopsis orthologs of DAXX or DEK that encode H3.3 chaperones in mammals (Sawatsubashi et al., 2010; Elsässer et al., 2012). "
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    ABSTRACT: In animals, replication-independent incorporation of nucleosomes containing the histone variant H3.3 enables global reprogramming of histone modifications and transcriptional profiles. H3.3 enrichment over gene bodies correlates with gene transcription in animals and plants. In animals, H3.3 is deposited into chromatin by specific protein complexes, including the HIRA complex. H3.3 variants evolved independently and acquired similar properties in animals and plants, questioning how the H3.3 deposition machinery evolved in plants and what are its biological functions. We performed phylogenetic analyses in the plant kingdom and identified in Arabidopsis all orthologs of human genes encoding members of the HIRA complex. Genetic analyses, biochemical data and protein localisation suggest that these proteins form a complex able to interact with H3.3 in Arabidopsis in a manner similar to that described in mammals. In contrast to animals, where HIRA is required for fertilization and early development, loss of function of HIRA in Arabidopsis causes mild phenotypes in the adult plant and does not perturb sexual reproduction and embryogenesis. Rather, HIRA function is required for transcriptional reprogramming during dedifferentiation of plant cells that precedes vegetative propagation and for the appropriate transcription of genes responsive to biotic and abiotic factors. We conclude that the molecular function of the HIRA complex is conserved between plants and animals. Yet plants diversified HIRA functions to enable asexual reproduction and responsiveness to the environment in response to the plant sessile lifestyle.
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    • "Remarkably, the absence of a glycine in the αC helix of H2A.Z, which is critical for Anp32e preferential recognition, is likely the major contributor to the conformational change. These observations further broaden our knowledge regarding histone variant selection34,35,36,37,38. It has previously been reported that the C-terminal region of H2A.Z is functionally essential in Drosophila and important for preferential binding of H2A.Z to the SWR1 complex and the Chz1 protein26,31. "
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    • "Swr1 Is a Chaperone for the H2A.Z-H2B Dimer 2008], Scm3 [Zhou et al., 2011], Daxx [Elsä sser et al., 2012; Liu et al., 2012], HJURP [Hu et al., 2011], and FACT [Hondele et al., 2013]). Using a previous assay for chaperone function of FACT on H2A-H2B (Hondele et al., 2013), we performed gel-shift experiments in order to examine the chaperone function of the Swr1-Z domain. "
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