Architecture of the Smc complexes. (A) The core of each Smc complex is formed by two Smc proteins. Each Smc protein contains an ATPase head domain, a hinge domain, and an intramolecular antiparallel coiled coil that connects the two. The hinge domain mediates the dimerization of Smc proteins. (B) Various Smc complexes found in bacteria and eukaryotes. Each Smc complex is composed of a specific Smc dimer and several non-Smc subunits. (i) The bacterial Smc complex from Bacillus subtilis. ScpA connects the two ATPase heads of the Smc homodimer. (ii) The Smc1/3 cohesin complex. (iii) The Smc5/6 complex. (iv) The condensin I complex. H, D2, and G stand for CAP-H, CAP-D2, and CAP-G, respectively. (v) The condensin II complex. H2, D3, and G2 stand for CAP-H2, CAP-D3, and CAP-G2, respectively. (vi) The condensin-like dosage compensation complex in C. elegans. DPY-27 is an Smc4 variant.