Rules of engagement for cohesin and condensin complexes during mitotic chromosome formation
During mitosis interphase chromatin is rapidly converted into rod-shaped mitotic chromosomes. Using Hi-C, imaging, proteomics, and polymer modeling we determine how the interplay between loop-extruding SMC motors accomplishes this dramatic transition. We find that condensin disassembles interphase chromatin loop organization by evicting or displacing extrusive cohesin. In contrast, condensins bypass cohesive cohesins, thereby maintaining sister chromatid cohesion while separating the sisters. We also estimate a speed of loop extrusion in vivo ~1-3 kb/sec. Our new models of mitotic chromosome conformation reveal that the loop organization by a discontinuous helical condensin II scaffold can vary greatly between chromosomes. We define a small set of rules of engagement for SMC complexes that together explain how cells refold interphase chromatin into mitotic chromosomes.