Accurate segregation of chromosomes is essential for continued viability of the products of cell division. Cells have developed sophisticated machinery and regulatory mechanisms to ensure that the events of mitosis happen in the correct order, and prevent progression if errors are detected. A key component for the pulling apart of identical DNA strands is the spindle. This apparatus is built primarily of polymers of α and β-tubulin, some of which form long filaments that attach to the DNA strands, and others that interact with each other to form a structure capable of withstanding the forces necessary to move large chromosomes around. The spindle is regulated by a large number of proteins, some that mainly effect the addition and removal of tubulin on the individual filaments, and others that can interact with the filaments to hold them together and move along them. The study of this dynamic structure is necessary to elucidate both the mechanisms of chromosome segregation, and the ways in which it can be disrupted and lead to missegregation events, a hallmark of cancerous cells.

This thesis focuses on the roles of one protein in the events of cell division; Slk19p of Saccharomyces cerevisiae. We determine that Slk19p has two functionally separable roles in division. First, Slk19p has been shown to be a member of the FEAR pathway, a protein network that activates a key regulator of both spindle dynamics and the progression of the cell cycle, Cdc14p. Separately, Slk19p performs at least one direct role in regulating the behavior of microtubules while they are pushing the chromosomes to opposite ends of the cell. We begin by showing these two functions are dependent on distinct domains of the protein, and then examine the effects on cell division when these domains are disrupted.