It never ceases to amaze me when there are new interactions discovered at the kinetochore, given how much attention is focused on it and how well-studied many of its components are. For example, two recent papers now show that the centromeric protein CENP-C, which has been scrutinized for at least a couple of decades, connects the inner and outer regions of the kinetochore.
Screpanti et al. show in human cells that the N-terminal region of Cenp-C binds directly and with high affinity to the Mis12 complex (which is part of the outer kinetochore KMN network of the protein complexes Mis12-Ndc80-Knl1). Cenp-C is part of the CCAN (constitutive centromere-associated network) and is a part of centromeric chromatin. Overexpression of the N-terminus of Cenp-C prevented the localization of the KMN network to kinetochores. Predictably, these cells had chromosome segregation and spindle assembly checkpoint defects. Meanwhile, Przewloka et al. show that each protein complex of the KMN network interacts with Cenp-C in flies, which lack many of the other proteins of the CCAN. These authors targeted the N-terminus of Cenp-C to centrosomes and this recruited the other complexes of the KMN network and of course caused segregation defects. So it seems that Cenp-C is the conserved connector between the inner and outer kinetochore.
For details on this series of posts, click here.