Background: Structural maintenance of chromosomes (SMC) and non-SMC condensin proteins associate into complexes that have been implicated in the process of chromosome condensation. A crucial prerequisite for accurate segregation of replicated sister chromatids is the condensation of the chromosomes into a manageable form prior to metaphase. The condensin I complex consists of two SMC subunits, SMC2 and SMC4, and three non-SMC subunits, CAP-H, CAP-G, and CAP-D2. An alternative complex, the condensin II complex, contains alternate non-SMC subunits, CAP-G2, CAP-H2, and CAP-D3. CAP-H2 is also known as Non-SMC condensin II complex, subunit H2 (NCAPH2) or kleisin beta isoform 2. The three non-SMC subunits in the condensing complexes form a regulatory subcomplex that is required to activate the SMC ATPases and to promote mitosis-specific chromatin binding of the holocomplex. The precise individual functions of each non-SMC protein in activation remain to be determined.