Crystal Structure of the Yeast Inner Kinetochore Subunit cep3p

Abstract

In budding yeast, the four-protein CBF3 complex (Skp1p-Ctf13p-Cep3p-Ndc10p) initiates kinetochore assembly by binding to the CDEIII locus of centromeric DNA. A Cep3p dimer recruits a Ctf13p-Skp1p heterodimer and contacts two sites on CDEIII. We report here the crystal structure, determined at 2.8 Å resolution by multiple isomorphous replacement with anomalous scattering, of a truncated Cep3p [Cep3p (47−608)], comprising all but an N-terminal, Zn2Cys6-cluster, DNAbinding module. Cep3p has a well-ordered structure throughout essentially all of its polypeptide chain, unlike most yeast transcription factors, including those with Zn2Cys6 clusters like Gal4p. This difference may reflect an underlying functional distinction: while any particular transcription factor must adapt to a variety of upstream activating sites, Cep3p scaffolds kinetochore assembly on centromeres uniformly configured on all 16 yeast chromosomes. We have, using the structure of Cep3p (47−603) and the known structures of Zn2Cys6 cluster domains, modeled the interaction of Cep3p with CDEIII.