Large-scale ATP-independent nucleosome unfolding by a histone chaperone

Abstract

DNA accessibility to regulatory proteins is significantly affected by nucleosome structure and dynamics. FACT (facilitates chromatin transcription) increases the accessibility of nucleosomal DNA but the mechanism and extent of this nucleosome reorganization are unknown. We report here the effects of FACT on single nucleosomes revealed with spFRET microscopy. FACT binding results in a dramatic, ATP-independent, and reversible uncoiling of DNA that affects at least 70% of the DNA in a nucleosome. A mutated version of FACT is defective in this uncoiling, and a histone mutation that suppresses phenotypes caused by this FACT mutation in vivo restores the uncoiling activity in vitro. Thus FACT-dependent nucleosome unfolding modulates the accessibility of nucleosomal DNA, and this is an important function of FACT in vivo.

Fly Fishing for Histones: Catch and Release by Histone Chaperone Intrinsically Disordered Regions and Acidic Stretches

“…Subsequent analyses demonstrated that FACT is a histone chaperone responsible for disassembly and reassembly of nucleosomes during transcription and DNA replication [74,75]. More recent single molecule FRET studies show that FACT binds to mono-nucleosomes and can induce partial uncoiling of nucleosomal DNA from histones, consistent with a role for FACT in activating transcription elongation through chromatinized DNA templates [76]. Structural studies on the FACT complex show that it is composed of four distinct domains: Spt16 N-terminal domain (Figure 4A), the dimerization domains of Spt16 and SSRP1, the middle domains of Spt16 and SSRP1 (Figures 4B and 4C, respectively), and the long C-terminal domains (CTD) of Spt16 and SSRP1, which are predicted to be disordered and have acidic stretches (Figure 3) [77–79].…”

Transcription promotes the interaction of the FAcilitates Chromatin Transactions (FACT) complex with nucleosomes inS. cerevisiae

“…However, it should be noted that multiple studies have shown that FACT can disrupt nucleosome structure in vitro (X in et al . 2009; V alieva et al . 2016), and thus we cannot rule out the possibility that FACT further alters chromatin structure once bound.…”

Mitotic Chromosome Assembly In Vitro: Functional Cross Talk between Nucleosomes and Condensins

“…Second, unique characteristics of H2A.X-F (e.g., its extended, acidic carboxyl terminus) could weaken or destabilize interactions between histones and DNA, consequently facilitating the productive action of topo II and/or condensin I on nucleosome arrays. A similar argument may also be applied to the action of the histone chaperone FACT, as recent structural studies suggested that FACT facilitates nucleosome reorganization by partially disrupting histone-DNA interactions (Hondele et al 2013;Kemble et al 2015;Tsunaka et al 2016;Valieva et al 2016). It is therefore reasonable to speculate that FACT confers structural flexibility on nucleosomes in the chromatid reconstitution reaction.…”