Chromosome segregation during mitosis requires assembly of the kinetochore complex at the centromere. Key to kinetochore assembly is the specific recognition of the histone variant CENP-A in the centromeric nucleosome by centromere protein C (CENP-C). We have defined the determinants of this recognition mechanism and discovered that CENP-C binds a hydrophobic region in the CENP-A tail and docks onto the acidic patch of histone H2A/H2B. We further find that the more broadly conserved CENP-C motif uses the same mechanism for CENP-A nucleosome recognition. Our findings reveal a conserved mechanism for protein recruitment to centromeres and a histone recognition mode whereby a disordered peptide binds the histone tail through nucleosome-docking-facilitated hydrophobic interactions.

Summary Linker histones bind to the nucleosome and regulate the structure of chromatin and gene expression. Despite more than three decades of effort, structural basis of nucleosome recognition by linker histones remains elusive. Here, we report the crystal structure of the globular domain of chicken linker histone H5 in complex with the nucleosome at 3.5 Å resolution, which is validated using nuclear magnetic resonance spectroscopy. The globular domain sits on the dyad of the nucleosome and interacts with both DNA linkers. Our structure integrates results from mutation analyses, previous cross-linking and fluorescence recovery after photobleach experiments, and helps resolve the long debate on structural mechanisms of nucleosome recognition by linker histones. The on-dyad binding mode of the H5 globular domain is different from the recently reported off-dyad binding mode of Drosophila linker histone H1. We demonstrate that linker histones with different binding modes could fold chromatin to form distinct higher-order structures.

The authors note that, due to a printer's error, references 41-50 appeared incorrectly. The corrected references follow. The authors note: "Our paper unfortunately missed reference to an earlier suggestion of the T6 structure (43). This work entitled 'A hypothetical dense 3,4-connected carbon net and related B 2 C and CN 2 nets built from 1,4-cyclohexadienoid units' by M. J. Bucknum and R. Hoffmann was published in J Am Chem Soc 116: 11456-11464 (1994), where the electronic structure of a hypothetical 3,4-connected tetragonal allotrope of carbon is discussed. The results in this article are consistent with what we find. The same group had also suggested a metallic carbon structure (44) that was published in J Am Chem Soc 105: 4831-4832 (1983), which we also missed to cite. We thank Prof. Hoffmann for bringing these papers to our attention."The complete references appear below. www.pnas.org/cgi