Mechanics, Structure and Dynamics of Metaphase Chromosome Folding

During cell division, eukaryote chromosomes are restructured from a relatively dispersed interphase form, into a relatively compact folded metaphase form. I will discuss experiments aimed at analyzing the folding scheme of metaphase chromosomes, where mechanical response and biochemical perturbation are used as tools for diagnosing structure. Experiments with nucleases reveal that the continuity of the metaphase chromosome depends on DNA, i.e., that the metaphase chromosome can be considered to be a ``chromatin gel.'' Experiments with topoisomerases indicate that chromatin entanglements play an appreciable role in determining chromosome mechanical properties, suggesting that they may play a structural role. We further show that perturbation of condensin complexes dramatically changes metaphase chromosome mechanics. Finally we report results of fluorescence visualization of distributions of condensin I and II along metaphase chromosomes.