Abstract
The core histone tail domains mediate inter-nucleosomal interactions that direct folding and condensation of nucleosome arrays into higher-order chromatin structures. The histone H4 tail domain facilitates inter-array interactions by contacting both the H2A/H2B acidic patch and DNA of neighboring nucleosomes. Likewise, H4 tail-H2A contacts stabilize array folding. However, whether the H4 tail domains stabilize array folding via inter-nucleosomal interactions with the DNA of neighboring nucleosomes remains unclear. We utilized defined oligonucleosome arrays containing a single specialized nucleosome with a photo-inducible cross-linker in the N terminus of the H4 tail to characterize these interactions. We observed that the H4 tail participates exclusively in intra-array interactions with DNA in unfolded arrays. These interactions are diminished during array folding, yet no inter-nucleosome, intra-array H4 tail-DNA contacts are observed in condensed chromatin. However, we document contacts between the N terminus of the H4 tail and H2A. Installation of acetylation mimics known to disrupt H4-H2A surface interactions did not increase observance of H4-DNA inter-nucleosomal interactions. These results suggest the multiple functions of the H4 tail require targeted distinct interactions within condensed chromatin.
Highlights
The core histone tail domains are essential for formation of native chromatin structures, but interactions are poorly understood
The H4 tail domain contacts an acidic patch comprised of histones H2A and H2B on the surface of neighboring nucleosomes to stabilize folding of nucleosome arrays into secondary chromatin structures [3]
Similar to the H3 tail, we find that the H4 tail exclusively participates in intra-nucleosome contacts to DNA within extended, unfolded arrays
Summary
The core histone tail domains are essential for formation of native chromatin structures, but interactions are poorly understood. The core histone tail domains mediate inter-nucleosomal interactions that direct folding and condensation of nucleosome arrays into higher-order chromatin structures. Previous work from our laboratory and others indicates that the histone H3 tails interact primarily with the DNA of the nucleosome from which they project, forming intra-nucleosomal interactions, when model nucleosome arrays exist as extended “beads-on-a-string” structures [16, 17]. Our data indicate that the H4 tail domain does not participate in inter-nucleosomal, intra-array interactions with DNA in folded, self-associated arrays. Installation of acetylation mimics within the histone H4 tail did not result in detectable inter-nucleosomal interactions with DNA These data are consistent with a model in which the histone H4 tail rearranges from intra-nucleosomal interactions with DNA in extended arrays to primarily inter-nucleosomal interactions with the H2A/H2B acidic pocket and inter-array interactions with both DNA and the acidic pocket in highly condensed chromatin structures
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