Abstract
DNA in the eukaryotic nucleus is not naked. Instead, it is complexed at frequent intervals with an equal molecular mass of histones to form nucleosomes. In the nucleosome, ∼146 bp of DNA are wrapped around a core histone octamer composed of two copies each of histones H4, H3, H2B, and H2A. The family of linker histones (H1, H5 and H1°) bind to the DNA between successive nucleosomes and help maintain the three-dimensional arrangement of nucleosomes within the chromatin fiber. AFM studies of chromatin fibers with the histones either selectively trypsinized or selectively reconstituted demonstrate a specific role for the H3 N-termini in maintaining fiber structure, in conjunction with the 80 amino acid linker histone globular domain. These AFM results structurally agree with the location of the H3 N-termini in the histone octamer or the nucleosome core particle.
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