Histone H1 Remains Bound to the Nucleosome Dyad During TF Binding within a Nucleosome

Abstract

H1 is a lysine rich histone that binds nucleosomes and alters nucleosome/chromatin dynamics. Chromatin dynamics, such as chromatin compaction and nucleosome unwrapping, are integral for regulation of fundamental cellular processes including transcription, DNA replication, and DNA repair. Nucleosomal DNA in the entry/exit region spontaneously dissociates from the histone octamer allowing transcription factors (TFs) to bind to DNA in the region when the nucleosome is in an unwrapped state. Instead of blocking wrapping, H1 shifts this equilibrium towards a wrapped state which represses TF binding without fully occluding it. Details of this TF binding mechanism remain unknown, including the structural dynamics of H1 domains during TF binding and which domains affect wrapping and TF binding. Using in vitro fluorescence‐based assays, we have determined the structural dynamics of H1 during TF binding to a nucleosome. H1 binds nucleosomes via electrostatic interactions with DNA and is composed of 3 domains: The winged helix domain that binds the nucleosome dyad and linker DNA, and the intrinsically disordered C terminal and N terminal domains that bind linker DNA. Previous work implied that H1 remains bound to a nucleosome during TF binding, but the details of H1 domain locations were unexplored. We have attached fluorophores and fluorophore quenchers to all 3 H1 domains and either the DNA or histone octamer to measure FRET and fluorophore quenching. This allows us to monitor the movement of the H1 domains relative to the DNA and histone octamer during TF binding. Our results indicate that H1 remains bound to the nucleosome dyad during a TF binding event, and the H1 C terminal domain dissociates from the linker DNA to remain at the dyad. These data further understanding of the mechanistic details of H1 suppression of TF binding to nucleosomes. Future experiments will focus on which H1 domains affect DNA wrapping and TF binding to a nucleosome to further understanding of how H1 regulates TF binding and the implications for transcription.Support or Funding InformationNIH R01‐GM121966NIH T32‐GM086252OSU University Fellowship