title: The FACT histone chaperone guides histone H4 into its nucleosomal conformation in Saccharomyces cerevisiae.
abstract: The pob3-Q308K mutation alters the small subunit of the Saccharomyces cerevisiae histone/nucleosome chaperone Facilitates Chromatin Transactions (FACT), causing defects in both transcription and DNA replication. We describe histone mutations that suppress some of these defects, providing new insight into the mechanism of FACT activity in vivo. FACT is primarily known for its ability to promote reorganization of nucleosomes into a more open form, but neither the pob3-Q308K mutation nor the compensating histone mutations affect this activity. Instead, purified mutant FACT complexes fail to release from nucleosomes efficiently, and the histone mutations correct this flaw. We confirm that pob3-T252E also suppresses pob3-Q308K and show that combining two suppressor mutations can be detrimental, further demonstrating the importance of balance between association and dissociation for efficient FACT:nucleosome interactions. To explain our results, we propose that histone H4 can adopt multiple conformations, most of which are incompatible with nucleosome assembly. FACT guides H4 to adopt appropriate conformations, and this activity can be enhanced or diminished by mutations in Pob3 or histones. FACT can therefore destabilize nucleosomes by favoring the reorganized state, but it can also promote assembly by tethering histones and DNA together and maintaining them in conformations that promote canonical nucleosome formation.
authors.affiliation: Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84112.
authors.forename: Laura
authors.initials: L
authors.lastname: McCullough
authors.forename: Bryan
authors.initials: B
authors.lastname: Poe
authors.forename: Zaily
authors.initials: Z
authors.lastname: Connell
authors.forename: Hua
authors.initials: H
authors.lastname: Xin
authors.forename: Tim
authors.initials: T
authors.lastname: Formosa
mesh_terms: D000595:Amino Acid Sequence; D056488:Histone Chaperones / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009707:Nucleosomes / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D056488:Histone Chaperones; D006657:Histones; D009707:Nucleosomes; C106768:POB3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors
keywords: FACT suppressor; histone mutations; histone rearrangement; nucleosome reorganization