Complex rheology of condensin in entangled DNA

Structural-Maintenance-of-Chromosome (SMC) complexes such as condensins are well-known to dictate the folding and entanglement of interphase and mitotic chromosomes. However, their role in modulating the rheology and viscoelasticity of entangled DNA is not fully understood. In this work, we discover that physiological concentrations of yeast condensin increase both the effective viscosity and elasticity of dense solutions of $\lambda$-DNA even in absence of ATP. By combining biochemical assays and single-molecule imaging, we discover that yeast condensin can proficiently bind double-stranded DNA through its hinge domain, in addition to its heads. We further discover that presence of ATP fluidifies the entangled solution possibly by activating loop extrusion. Finally, we show that the observed rheology can be understood by modelling SMCs as transient crosslinkers in bottle-brush-like entangled polymers. Our findings help us to understand how SMCs affect the rheology and dynamics of the genome.