Bacterial chromosome organization by collective dynamics of SMC condensins

Recent Hi-C experiments of many bacterial species indicate a juxtaposed organization of the two chromosomal arms. These features in Hi-C maps have been attributed to various nucleoid-associated proteins, including the highly conserved SMC condensin. Although the molecular structure of these ATPases has been mapped in detail, it has been unclear how only a small number of condensins orchestrates this remarkable spatial organization. To resolve this puzzle, we developed a computational model for the dynamic organization of DNA by condensins as active slip-links. We first consider a scenario in which the ATPase activity of slip-links regulates their DNA-recruitment near the origin of replication, while the slip-link dynamics is assumed to be purely diffusive. We find that such diffusive slip-links can organize the entire chromosome into a state with aligned arms, but not within physiological constraints. However, slip-links that include motor activity are far more effective at organizing the entire chromosome, dynamically driving an entire chromosome into the juxtaposed state at physiological densities. We expand on these insights by showing the relation between this out-of-equilibrium organization and chromosome segregation.