title: The activity of the histone chaperone yeast Asf1 in the assembly and disassembly of histone H3/H4-DNA complexes.
abstract: The deposition of the histones H3/H4 onto DNA to give the tetrasome intermediate and the displacement of H3/H4 from DNA are thought to be the first and the last steps in nucleosome assembly and disassembly, respectively. Anti-silencing function 1 (Asf1) is a chaperone of the H3/H4 dimer that functions in both of these processes. However, little is known about the thermodynamics of chaperone-histone interactions or the direct role of Asf1 in the formation or disassembly of histone-DNA complexes. Here, we show that Saccharomyces cerevisiae Asf1 shields H3/H4 from unfavorable DNA interactions and aids the formation of favorable histone-DNA interactions through the formation of disomes. However, Asf1 was unable to disengage histones from DNA for tetrasomes formed with H3/H4 and strong nucleosome positioning DNA sequences or tetrasomes weakened by mutant (H3K56Q/H4) histones or non-positioning DNA sequences. Furthermore, Asf1 did not associate with preformed tetrasomes. These results are consistent with the measured affinity of Asf1 for H3/H4 dimers of 2.5 nM, which is weaker than the association of H3/H4 for DNA. These studies support a mechanism by which Asf1 aids H3/H4 deposition onto DNA but suggest that additional factors or post-translational modifications are required for Asf1 to remove H3/H4 from tetrasome intermediates in chromatin.
authors: Department of Pharmacology, University of Colorado, School of Medicine, Aurora, CO 80045, USA.
authors: Douglas C
authors: DC
authors: Donham
authors: Jean K
authors: JK
authors: Scorgie
authors: Mair E A
authors: ME
authors: Churchill
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D024243:HMGB1 Protein / Q000378:metabolism; D006657:Histones / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: C109731:ASF1 protein, S cerevisiae; D018797:Cell Cycle Proteins; D024243:HMGB1 Protein; D006657:Histones; D018832:Molecular Chaperones; D009707:Nucleosomes; D029701:Saccharomyces cerevisiae Proteins; D004247:DNA