LAUSR

Recognizing centromere by kinetochore The kinetochore proteins CENP-N and CENP-C recognize the histone H3 variant CENP-A in the centromeric nucleosome. This ensures proper kinetochore assembly and accurate segregation of chromosomes. Chittori et al. describe the cryo-electron microscopy structure of the human CENP-A nucleosome-CENP-N complex. The interaction of CENP-N with CENP-A and the nucleosomal DNA together ensure specific and stable centromeric nucleosome recognition. Mutational analyses using both human and Xenopus CENP-A and CENP-N proteins suggest that the proteins have coevolved to preserve the interacting surfaces. Science, this issue p. 339 Cryo–electron microscopy reveals mechanisms of centromeric nucleosome recognition and initial assembly steps of the kinetochore complex. Accurate chromosome segregation requires the proper assembly of kinetochore proteins. A key step in this process is the recognition of the histone H3 variant CENP-A in the centromeric nucleosome by the kinetochore protein CENP-N. We report cryo–electron microscopy (cryo-EM), biophysical, biochemical, and cell biological studies of the interaction between the CENP-A nucleosome and CENP-N. We show that human CENP-N confers binding specificity through interactions with the L1 loop of CENP-A, stabilized by electrostatic interactions with the nucleosomal DNA. Mutational analyses demonstrate analogous interactions in Xenopus, which are further supported by residue-swapping experiments involving the L1 loop of CENP-A. Our results are consistent with the coevolution of CENP-N and CENP-A and establish the structural basis for recognition of the CENP-A nucleosome to enable kinetochore assembly and centromeric chromatin organization.