title: The histone variant macro-H2A preferentially forms "hybrid nucleosomes".
abstract: The histone domain of macro-H2A, which constitutes the N-terminal one third of this histone variant, is only 64% identical to major H2A. We have shown previously that the main structural differences in a nucleosome in which both H2A moieties have been replaced by macro-H2A reside in the only point of contact between the two histone dimers, the L1-L1 interface of macro-H2A. Here we show that the L1 loop of macro-H2A is responsible for the increased salt-dependent stability of the histone octamer, with implications for the nucleosome assembly pathway. It is unknown whether only one or both of the H2A-H2B dimers within a nucleosome are replaced with H2A variant containing nucleosomes in vivo. We demonstrate that macro-H2A preferentially forms hybrid nucleosomes containing one chain each of major H2A and macro-HA in vitro. The 2.9-A crystal structure of such a hybrid nucleosome shows significant structural differences in the L1-L1 interface when comparing with homotypic major H2A- and macro-H2A-containing nucleosomes. Both homotypic and hybrid macro-nucleosome core particles (NCPs) are resistant to chaperone-assisted H2A-H2B dimer exchange. Together, our findings suggest that the histone domain of macro-H2A modifies the dynamic properties of the nucleosome. We propose that the possibility of forming hybrid macro-NCP adds yet another level of complexity to variant nucleosome structure and function.
authors.affiliation: Howard Hughes Medical Institute and Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523-1870, USA.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Chakravarthy
authors.forename: Karolin
authors.initials: K
authors.lastname: Luger
mesh_terms: D000818:Animals; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray; D019281:Dimerization; D005656:Fungal Proteins / Q000378:metabolism; D006657:Histones / Q000737:chemistry*; D051379:Mice; D008958:Models, Molecular; D009707:Nucleosomes / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014982:Xenopus laevis
chemical_list: D005656:Fungal Proteins; D006657:Histones; D009707:Nucleosomes