Li Sha, Edwards Garrett, Radebaugh Catherine A, Luger Karolin, Stargell Laurie A
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, USA; Department of Biochemistry, University of Colorado, Boulder, CO 80309, USA.
Department of Biochemistry, University of Colorado, Boulder, CO 80309, USA.
J Mol Biol. 2022 Jul 15;434(13):167630. doi: 10.1016/j.jmb.2022.167630. Epub 2022 May 18.
Histone chaperones facilitate the assembly and disassembly of nucleosomes and regulate DNA accessibility for critical cellular processes. Spn1 is an essential, highly conserved histone chaperone that functions in transcription initiation and elongation in a chromatin context. Here we demonstrate that Spn1 binds H3-H4 with low nanomolar affinity, residues 85-99 within the acidic N-terminal region of Spn1 are required for H3-H4 binding, and Spn1 binding to H3-H4 dimers does not impede (H3-H4) tetramer formation. Previous work has shown the central region of Spn1 (residues 141-305) is important for interaction with Spt6, another conserved and essential histone chaperone. We show that the C-terminal region of Spn1 also contributes to Spt6 binding and is critical for Spn1 binding to nucleosomes. We also show Spt6 preferentially binds H3-H4 tetramers and Spt6 competes with nucleosomes for Spn1 binding. Combined with previous results, this indicates the Spn1-Spt6 complex does not bind nucleosomes. In contrast to nucleosome binding, we found that the Spn1-Spt6 complex can bind H3-H4 dimers and tetramers and H2A-H2B to form ternary complexes. These important results provide new information about the functions of Spn1, Spt6, and the Spn1-Spt6 complex, two essential and highly conserved histone chaperones.
组蛋白伴侣蛋白促进核小体的组装与拆卸，并调节关键细胞过程中DNA的可及性。Spn1是一种必需的、高度保守的组蛋白伴侣蛋白，在染色质环境下的转录起始和延伸过程中发挥作用。在此，我们证明Spn1以低纳摩尔亲和力结合H3-H4，Spn1酸性N端区域内的85-99位残基是H3-H4结合所必需的，且Spn1与H3-H4二聚体的结合并不妨碍（H3-H4）四聚体的形成。先前的研究表明，Spn1的中央区域（141-305位残基）对于与另一种保守且必需的组蛋白伴侣蛋白Spt6的相互作用很重要。我们发现Spn1的C端区域也有助于与Spt6结合，并且对于Spn1与核小体的结合至关重要。我们还表明，Spt6优先结合H3-H4四聚体，并且Spt6与核小体竞争Spn1的结合。结合先前的结果，这表明Spn1-Spt6复合物不结合核小体。与核小体结合不同，我们发现Spn1-Spt6复合物可以结合H3-H4二聚体和四聚体以及H2A-H2B以形成三元复合物。这些重要结果提供了关于Spn1、Spt6以及Spn1-Spt6复合物（两种必需且高度保守的组蛋白伴侣蛋白）功能的新信息。
