{'fraction_non_alphanumeric': 0.022996057818659658, 'fraction_numerical': 0.0045992115637319315, 'mean_word_length': 5.5085470085470085, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
The CENP‐A Targeting Domain (CATD) Confers Conformational Rigidity to Centromeric Nucleosomes and Plays an Essential Role at Mitosis

While the physical nature of the epigenetic mark defining the location of the centromere on the chromosome is not known, nucleosomes in which CENP‐A replaces histone H3 are at the foundation of the centromeric chromatin. Hydrogen/deuterium exchange mass spectrometry is now used to show that assembly into nucleosomes imposes stringent conformational constraints, reducing solvent accessibility in almost all histone regions by >3 orders of magnitude. Nucleosomes assembled with CENP‐A are substantially more conformationally rigid than those assembled with histone H3, independent of DNA template. Substitution of the CATD, comprised of the loop 1 and α2 helix of the CENP‐A histone fold domain, into histone H3 generates the same more rigid nucleosome as does CENP‐A. In human cells, while depletion of CENP‐A is lethal, recruitment of normal levels of kinetochore proteins, centromere‐generated mitotic checkpoint signaling, normal chromosome segregation and viability can be rescued by this chimeric H3 containing the CATD. The CATD, itself, is confined to the structured “core”" of the nucleosome demonstrating that much (if not all) of the essential features of CENP‐A are within the rigid core of the nucleosome. These data support a model of centromere identity maintained by a unique nucleosome structure that serves to distinguish the centromere from the rest of the chromosome.