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Nucleic Acids Res 2011 Jul 01;3913:5449-58. doi: 10.1093/nar/gkr097.
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The activity of the histone chaperone yeast Asf1 in the assembly and disassembly of histone H3/H4-DNA complexes.

Donham DC , Scorgie JK , Churchill ME .

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.

PubMed ID: 21447559
PMC ID: PMC3141235
Article link: Nucleic Acids Res
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: asf1a hmgb1 nps

Article Images: [+] show captions
References [+] :
Adkins, Chromatin disassembly mediated by the histone chaperone Asf1 is essential for transcriptional activation of the yeast PHO5 and PHO8 genes. 2004, Pubmed