Effects of histone acetylation, ubiquitination and variants on nucleosome stability.
The properties of the nucleosomes of a salt-soluble, transcriptionally active gene-enriched fraction of chicken erythrocyte chromatin were evaluated by hydroxyapatite dissociation chromatography. We have demonstrated previously that the salt-soluble, transcriptionally active gene-enriched polynucleosomes are enriched in dynamically acetylated and ubiquitinated histones, and in an atypical U-shaped nucleosome that possessed about 20% less protein than a typical nucleosome. Further, newly synthesized histones H2A and H2B exchange preferentially with the nucleosomal histones H2A and H2B of this salt-soluble chromatin fraction. Analysis of the histones eluting from the hydroxyapatite-bound chromatin demonstrated that hyperacetylated and ubiquitinated (u), including multi-ubiquitinated, H2A-H2B.1 dimers dissociated at lower concentrations of NaCl than unmodified dimers or dimers with histone variants H2A.Z and/or H2B.2. Cross-linking studies revealed that at least 50% of uH2B.1 was paired with uH2A. uH2A-uH2B.1 dimers dissociated at lower NaCl concentrations than H2A-uH2B.1 dimers. Hyperacetylated histone (H3-H4)2 tetramers also eluted at lower concentrations of NaCl than unmodified tetramers. Our results support the idea that acetylation and ubiquitination of histones H2A and H2B.1 increase the lability of H2A-H2B.1 dimers in transcriptionally active nucleosomes. In contrast, our observations suggest that histone variants H2A.Z and H2B.2. stabilize the association of the H2A-H2B dimer in nucleosomes. The elevated lability of the H2A-H2B dimer may facilitate processes such as the exchange of these dimers with newly synthesized histones, the elongation process of transcription and transcription factor binding.
Li
W
W
Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Nagaraja
S
S
Delcuve
G P
GP
Hendzel
M J
MJ
Davie
J R
JR
D000107:Acetylation; D000818:Animals; D002645:Chickens; D002843:Chromatin / Q000378:metabolism; D002853:Chromatography, Liquid; D003432:Cross-Linking Reagents; D017886:Durapatite; D004591:Electrophoresis, Polyacrylamide Gel; D006657:Histones / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism*
D002843:Chromatin; D003432:Cross-Linking Reagents; D006657:Histones; D009707:Nucleosomes; D014452:Ubiquitins; D017886:Durapatite