Association of condensin with chromosomes depends on DNA binding by its HEAT-repeat subunits

Condensin complexes have central roles in the three-dimensional organization of chromosomes during cell divisions, but how they interact with chromatin to promote chromosome segregation is largely unknown. Previous work has suggested that condensin, in addition to encircling chromatin fibers topologically within the ring-shaped structure formed by its SMC and kleisin subunits, contacts DNA directly. Here we describe the discovery of a binding domain for double-stranded DNA formed by the two HEAT-repeat subunits of the Saccharomyces cerevisiae condensin complex. From detailed mapping data of the interfaces between the HEAT-repeat and kleisin subunits, we generated condensin complexes that lack one of the HEAT-repeat subunits and consequently fail to associate with chromosomes in yeast and human cells. The finding that DNA binding by condensin's HEAT-repeat subunits stimulates the SMC ATPase activity suggests a multistep mechanism for the loading of condensin onto chromosomes.