Abstract
FACT is a histone chaperone that participates in nucleosome removal and reassembly during transcription and replication. We used electron microscopy to study FACT, FACT:Nhp6 and FACT:Nhp6:nucleosome complexes, and found that all complexes adopt broad ranges of configurations, indicating high flexibility. We found unexpectedly that the DNA binding protein Nhp6 also binds to the C-terminal tails of FACT subunits, inducing more open geometries of FACT even in the absence of nucleosomes. Nhp6 therefore supports nucleosome unfolding by altering both the structure of FACT and the properties of nucleosomes. Complexes formed with FACT, Nhp6, and nucleosomes also produced a broad range of structures, revealing a large number of potential intermediates along a proposed unfolding pathway. The data suggest that Nhp6 has multiple roles before and during nucleosome unfolding by FACT, and that the process proceeds through a series of energetically similar intermediate structures, ultimately leading to an extensively unfolded form.
Highlights
FACT is a histone chaperone that participates in nucleosome removal and reassembly during transcription and replication
HMGB-domain factors are basic proteins that bind to and bend DNA23, and titration of DNA with Nhp[6] produces a pattern of migration similar to the one shown in Fig. 1b, with multiple intermediates corresponding to gradual saturation of binding sites
As H2A/H2B24 and Nhp[6] (Fig. 1) can both bind to the C-terminal tails of FACT and to DNA, we propose that they swap partners, with the C-terminal tails taking the H2A-H2B binding site that had been occupied by DNA, and Nhp[6] moving to the DNA surface that had been bound by H2AH2B
Summary
FACT is a histone chaperone that participates in nucleosome removal and reassembly during transcription and replication. Complexes formed with FACT, Nhp[6], and nucleosomes produced a broad range of structures, revealing a large number of potential intermediates along a proposed unfolding pathway. 1234567890():,; The eukaryotic genome is densely packed into nucleosomes, each containing 145–147 bp of DNA1,2 This packing blocks the accessibility of the DNA to many of the proteins that control gene expression, with access tightly regulated by many factors including ATP-dependent remodelers and ATPindependent histone chaperones[3,4,5,6]. Spt[16] and Pob3/SSRP1 are organized into multiple, flexibly associated structural domains that contain several binding sites for H3/H4 tetramers and H2A/ H2B dimers, so FACT can interact simultaneously with all of the components of nucleosomes Spt[16] and Pob3/SSRP1 are organized into multiple, flexibly associated structural domains that contain several binding sites for H3/H4 tetramers and H2A/ H2B dimers, so FACT can interact simultaneously with all of the components of nucleosomes (see refs. 4–6 for review)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
