Focal localization of MukBEF condensin on the chromosome requires the flexible linker region of MukF.

Condensin complexes are the key mediators of chromosome condensation. The MukB-MukE-MukF complex is a bacterial condensin, in which the MukB subunit forms a V-shaped dimeric structure with two ATPase head domains. MukE and MukF together form a tight complex, which binds to the MukB head via the C-terminal winged-helix domain (C-WHD) of MukF. One of the two bound C-WHDs of MukF is forced to detach from two ATP-bound, engaged MukB heads, and this detachment reaction depends on the MukF flexible linker preceding the C-WHD. Whereas MukB is known to focally localize at particular positions in cells by an unknown mechanism, mukE- or mukF-null mutation causes MukB to become dispersed in cells. Here, we report that mutations in MukF causing a defect in the detachment reaction interfere with the focal localization of MukB, and that the dispersed distribution of MukB in cells correlates directly with defects in cell growth and division. The data strongly suggest that the MukB-MukE-MukF condensin forms huge clusters through the ATP-dependent detachment reaction, and this cluster formation is critical for chromosome condensation by this machinery. We also show that the MukF flexible linker is involved in the dimerization and ATPase activity of the MukB head.