An interdependent Cbf1-CCAN interaction stabilizes the budding yeast kinetochore

Abstract

Chromosome segregation requires the proper assembly of kinetochores on centromeric DNA. The kinetochore is a complex multi-protein machine comprising more than 40 distinct proteins, but the functional roles of many components remain unclear. One such protein is the yeast transcription factor Cbf1, which directly binds to budding yeast centromeric DNA. Loss of Cbf1 significantly increases the rate of chromosome missegregation, however its precise molecular mechanism of action is unknown. It was recently found that Cbf1 inhibits transcription through the centromere by preventing the untimely pericentromeric transcriptional readthrough via a roadblock mechanism. Intriguingly, restoring the transcriptional roadblock in the absence of Cbf1 binding only partially rescued chromosome missegregation, indicating that Cbf1 performs additional centromeric activities. Here, we show that Cbf1 promotes inner kinetochore assembly both in vitro and in vivo. This assembly function depends on the interface between Cbf1 and Okp1. Moreover, we found that the stable association of Cbf1 with the centromere requires its interaction with the inner kinetochore, revealing an interdependent interaction essential for the assembly and stability of the kinetochore. Thus, Cbf1 functions as a centromere-anchored hub that couples transcriptional roadblocking to CCAN assembly and kinetochore stability.