Eic1 links Mis18 with the CCAN/Mis6/Ctf19 complex to promote CENP-A assembly

Abstract

CENP-A chromatin forms the foundation for kinetochore assembly. Replication-independent incorporation of CENP-A at centromeres depends on its chaperone HJURP Scm3 , and Mis18 in vertebrates and fission yeast. The recruitment of Mis18 and HJURP Scm3 to centromeres is cell cycle regulated. Vertebrate Mis18 associates with Mis18BP1 KNL2 , which is critical for the recruitment of Mis18 and HJURP Scm3 . We identify two novel fission yeast Mis18-interacting proteins (Eic1 and Eic2), components of the Mis18 complex. Eic1 is essential to maintain Cnp1 CENP-A at centromeres and is crucial for kinetochore integrity; Eic2 is dispensable. Eic1 also associates with Fta7 CENP-Q/Okp1 , Cnl2 Nkp2 and Mal2 CENP-O/Mcm21 , components of the constitutive CCAN/Mis6/Ctf19 complex. No Mis18BP1 KNL2 orthologue has been identified in fission yeast, consequently it remains unknown how the key Cnp1 CENP-A loading factor Mis18 is recruited. Our findings suggest that Eic1 serves a function analogous to that of Mis18BP1 KNL2 , thus representing the functional counterpart of Mis18BP1 KNL2 in fission yeast that connects with a module within the CCAN/Mis6/Ctf19 complex to allow the temporally regulated recruitment of the Mis18/Scm3 HJURP Cnp1 CENP-A loading factors. The novel interactions identified between CENP-A loading factors and the CCAN/Mis6/Ctf19 complex are likely to also contribute to CENP-A maintenance in other organisms.