Structural insights into the role of the Chl4-Iml3 complex in kinetochore assembly

Human CENP-N and CENP-L have been reported to selectively recognize the CENP-A nucleosome and to contribute to recruiting other constitutive centromere-associated network (CCAN) complexes involved in assembly of the inner kinetochore. As their homologues, Chl4 and Iml3 from budding yeast function in a similar way in de novo assembly of the kinetochore. A lack of biochemical and structural information precludes further understanding of their exact role at the molecular level. Here, the crystal structure of Iml3 is presented and the structure shows that Iml3 adopts an elongated conformation with a series of intramolecular interactions. Pull-down assays revealed that the C-terminal domain of Chl4, which forms a dimer in solution, is responsible for Iml3 binding. Acting as a heterodimer, the Chl4-Iml3 complex exhibits a low-affinity nonspecific DNA-binding activity which may play an important role in the kinetochore-assembly process.