Abstract: The function of mitosis is to accurately segregate a duplicated cellular genome into two daughter cells. The goal of my research has been to understand the global contributions of chromatin to spindle assembly, anaphase and other mitotic functions using Xenopus egg extracts. First, I characterized the condensin complex; a key factor in the organization of higher order mitotic chromatin structure, an ideal candidate in which to elucidate the role of chromosome architecture in spindle assembly and function. Depletion of this complex from Xenopus egg extracts resulted in severe defects in chromosome morphology and reduced the fidelity of sperm spindle assembly. Additionally, it was required for the segregation of chromosomes during anaphase. Inhibition of condensin function at various times during the cell cycle determined that this complex is vital for the establishment and maintenance of chromosome condensation. The kinetochore component CENP-E was recruited to its proper position at the chromosome-microtubule interface but appeared stretched. These defects in kinetochore morphology were due to tension imparted upon sister kinetochores by microtubules because depolymerization of tubulin by nocodazole treatment restored normal CENP-E staining patterns. These results taken together indicate a requirement for the condensin complex in chromosome packaging, spindle assembly and chromosome segregation during mitosis. To further understand the function of chromatin in mitosis, I characterized the cohesin complex in Xenopus egg extracts. Depletion of cohesin from Xenopus egg extracts impairs sister chromatid cohesion and kinetochore-microtubule interactions, causing defective spindle attachments and chromosome alignment during metaphase, and mis-segregation during anaphase. In the absence of cohesin, sister kinetochore pairing and centromeric localization of chromosomal passenger proteins Incenp and Aurora B was lost upon bipolar spindle attachment. However, kinetochores remained paired with normal passenger localization if bipolar spindle formation was prevented by inhibiting the Kinesin-5 motor Eg5. These observations indicate that cohesin is not solely responsible for the establishment of sister chromatid cohesion, but is necessary to maintain cohesion and amphitelic attachment in the presence of bipolar spindle forces. (Abstract shortened by UMI.)