Shaping the metaphase chromosome: coordination of cohesion and condensation

Recent progress in our understanding of mitotic chromosome dynamics has bee n accelerated by the identification of two essential protein complexes, coh esin and condensin. Cohesin is required for holding sister chromatids (dupl icated chromosomes) together from S phase until the metaphase-to-anaphase t ransition. Condensin is a central player in chromosome condensation, a proc ess that initiates at the onset of mitosis. The main focus of this review i s to discuss how the mitotic metaphase chromosome is assembled and shaped b y a precise balance between the cohesion and condensation machineries. We a rgue that, in different eukaryotic organisms, the balance of cohesion and c ondensation is adjusted in such a way that the size and shape of the result ing chromosomes are best suited for their accurate segregation. (C) 2001 Jo hn Wiley & Sons, Inc.