A Molecular Basis for the Coupling of Sister Centromeres

Abstract

Chromosome segregation during mitosis requires that two forces act on DNA: one that pulls chromatids away from each other and towards presumptive daughter cells, and another that holds chromatids together and resists the first force. These forces converge on the centromere, a specialized region of the chromosome upon which is built the kinetochore, a multi-protein apparatus that connects spindle microtubules to DNA. Kinetochores participate in a signaling pathway that recruits the molecular agents of sister chromatid cohesion, protein complexes called cohesins, to centromeres. The accumulation of cohesin complexes at centromeres is required to resist spindle forces until anaphase, thereby ensuring efficient chromosome segregation. In this thesis, we describe the molecular events that conspire to recruit cohesin complexes to centromeres. This work presented here shows that the protein complex that loads cohesin onto chromosomes recognizes centromeres, a function that depends on Dbf4-dependent kinase (DDK) phosphorylation of the Ctf19 kinetochore protein. We also describe the reconstitution and analysis of factors that ensure proper cohesin loading. These studies provide a molecular explanation for the connection between sister centromeres and its regulation during the cell division cycle.