Functional and physical interactions between the condensin MukBEF and the decatenase Topo IV in E. coli. (A) Conceptual framework of how condensin and decatenase might collaborate to separate sister DNAs efficiently. (B) Model of how condensin might physically interact with Topo IV. The E. coli–condensin complex is composed of three subunits: MukB, MukE, and MukF (15). The MukB dimer (blue) is a large V-shaped molecule composed of two coiled-coil arms with ATP-binding “head” domains at their distal ends (5). The “hinge” domain, located at another end of each arm, mediates MukB's dimerization. The regulatory subunits MukE and MukF (light blue) associate with the head domains to link them within the same complex or between two different complexes. Topo IV is composed of two copies of ParC (green) and two copies of ParE (yellow) (6, 7). According to the current studies (1, 2), the hinge domain of MukB directly interacts with the CTD of ParC and stimulates the activities of Topo IV. The condensin complex and the decatenase enzyme could form a higher order assembly either in the presence or absence of DNA. Shown here is an example of putative arrangements as proposed by Li et al. (2).