Structure and dynamics of 2x(CENP-A/H4) ₂ octasome reveal a possible intermediate in centromeric chromatin

The centromere is a part of the chromosome that is essential for the even segregation of duplicated chromosomes during cell division. It is epigenetically defined by the presence of the histone H3 variant CENP-A. CENP-A associates specifically with a group of 16 proteins that form the constitutive centromere-associated network (CCAN) of proteins. In mitosis, the kinetochore forms on the CCAN to connect the duplicated chromosomes to the microtubules protruding from the cell poles. Previous studies have shown that CENP-A replaces H3 in nucleosomes, and recently, the structures of CENP-A-containing nucleosomes in complex with CCANs have been revealed, but they show only a limited interaction between CCANs and CENP-A. Here, we report the cryo-EM structure of 2x(CENP-A/H4)₂ octasomes assembled on DNA in the absence of H2A/H2B histone dimer and speculate how (CENP-A/H4)₂ tetrasomes might serve as a platform for CCAN organization.