Architecture of SMC-kleisin complexes

In all cellular systems, the transmission of bulk genetic information during proliferation occurs in the form of chromosomes. The segregation of these entities upon cell division is of pivotal importance for all forms of life. Structural maintenance of chromosomes (SMC)-kleisin complexes are ubiquitous and essential factors that ensure proper organisation and segregation of the genetic material. Aim of this work was to elucidate evolutionary conserved features in the architecture of SMC-kleisin complexes, and to probe these features for functional relevance. We find that two major architectural themes have been constrained by evolution: (I) SMC-kleisin complexes form asymmetric assemblies with a ring-like topology, whereby a kleisin monomer bridges two different binding sites on a SMC dimer, (II) SMC-kleisin complexes form rod-like structures, whereby the SMC proteins of a given dimer are closely juxtaposed in a well-defined manner. Based on these findings, we propose that SMC-kleisin complexes from all domains of life act by a unifying mechanism.