biostudies-literatureForte GEuropean Research CouncilWellcome Truste202209113https://www.ebi.ac.uk/biostudies/studies/S-EPMC10655892biostudies-literatureUnknown223(1)Eukaryotic chromosomes compact during mitosis into elongated cylinders-and not the spherical globules expected of self-attracting long flexible polymers. This process is mainly driven by condensin-like proteins. Here, we present Brownian-dynamic simulations involving two types of such proteins with different activities. One, which we refer to as looping condensins, anchors long-lived chromatin loops to create bottlebrush structures. The second, referred to as bridging condensins, forms multivalent bridges between distant parts of these loops. We show that binding of bridging condensins leads to the formation of shorter and stiffer mitotic-like cylinders without requiring any additional energy input. These cylinders have several features matching experimental observations. For instance, theThe Journal of cell biologyBridging condensins mediate compaction of mitotic chromosomes.PMC10655892223097/Z/21/Z648050Conforto FCook PRMarenduzzo DForte GGilbert NBoteva LfalseBridging condensins mediate compaction of mitotic chromosomes.Eukaryotic chromosomes compact during mitosis into elongated cylinders-and not the spherical globules expected of self-attracting long flexible polymers. This process is mainly driven by condensin-like proteins. Here, we present Brownian-dynamic simulations involving two types of such proteins with different activities. One, which we refer to as looping condensins, anchors long-lived chromatin loops to create bottlebrush structures. The second, referred to as bridging condensins, forms multivalent bridges between distant parts of these loops. We show that binding of bridging condensins leads to the formation of shorter and stiffer mitotic-like cylinders without requiring any additional energy input. These cylinders have several features matching experimental observations. For instance, the2024-01-01T00:00:00Z2024 Jan2025-04-22T18:00:25.34Z2025-04-06T02:21:01.086ZS-EPMC106558923797609110.1083/jcb.202209113