Abstract
The cohesin complex shapes the 3D genome by looping together regulatory elements along chromosomes. We find that chromatin loop size can be increased, and that the duration with which cohesin embraces DNA determines the degree to which loops are enlarged. Our data support the model that cohesin structures chromosomes through the processive enlargement of loops, and that this counteracts nuclear compartmentalization. We conclude that the balanced activity of SCC2/NIPBL-dependent loop extension, and WAPL-mediated DNA release, allows cohesin to correctly structure chromosomes.