The mammalian centromere: structural domains and the attenuation of chromatin modeling

The centromere-kinetochore complex can be divided into distinct domains bas ed on structure and function. Previous work has used CREST auto-antibodies with various microscopic techniques to map the locations of proteins within the centromere-kinetochore complex and to analyze the maturation of prekin etochores before mitosis, Here we have focused on the centromere-specific h istone Centromere Protein (CENP)-A and its spatial relationship to other hi stones and histone modifications found in condensed chromatin. We demonstra te that the phosphorylation of histone H3 is essentially excluded from a sp ecific region of centromeric chromatin, defined by the presence of CENP-A, Interspersion of CENP-B with phosphorylated H3 in the inner centromere indi cates that the exclusion of H3 modification is not a general property of cc -satellite DNA, We also demonstrate that these regions are functionally dis tinct by fragmenting mitotic chromatin into motile centromere-kinetochore f ragments that contain CENP-A with little or no phosphorylated H3 and nonmot ile fragments that contain exclusively phosphorylated H3, The sequence of C ENP-A diverges from H3 in a number of key residues involved in chromosome c ondensation and in transcription, potentially allowing a more specialized c hromatin structure within centromeric heterochromatin, on which kinetochore plates may nucleate and mature. This specialized centromere subdomain woul d be predicted to have a very tight and static nucleosome structure as a re sult of the absence of H3 phosphorylation and acetylation.