The SWR complex edits the histone composition of nucleosomes at promoters to facilitate transcription by replacing the two nucleosomal H2A-H2B (A-B) dimers with H2A.Z-H2B (Z-B) dimers. Swc5, a subunit of SWR, binds to A-B dimers, but its role in the histone replacement reaction was unclear ...
The SWR complex edits the histone composition of nucleosomes at promoters to facilitate transcription by replacing the two nucleosomal H2A-H2B (A-B) dimers with H2A.Z-H2B (Z-B) dimers. Swc5, a subunit of SWR, binds to A-B dimers, but its role in the histone replacement reaction was unclear. In this study, we showed that Swc5 uses a tandem DEF/Y motif within an intrinsically disordered region to engage the A-B dimer. A 2.37-Å X-ray crystal structure of the histone binding domain of Swc5 in complex with an A-B dimer showed that consecutive acidic residues and flanking hydrophobic residues of Swc5 form a cap over the histones, excluding histone-DNA interaction. Mutations in Swc5 DEF/Y inhibited the nucleosome editing function of SWR in vitro. Swc5 DEF/Y interacts with histones in vivo, and the extent of this interaction is dependent on the remodeling ATPase of SWR, supporting a model in which Swc5 acts as a wedge to promote A-B dimer eviction. Given that DEF/Y motifs are found in other evolutionary unrelated chromatin regulators, this work provides the molecular basis for a general strategy used repeatedly during eukaryotic evolution to mobilize histones in various genomic functions.
Organizational Affiliation:
University of Chinese Academy of Sciences, 100049 Beijing, China.
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