The structure and function of SMC-kleisin complexes

The accurate inheritance of the complete genetic information from one generation to another is the basis for the continuity of life. Protein complexes consisting of Structural Maintenance of Chromosomes (SMC) and kleisin subunits are central players assuring the proper segregation of a cell’s chromosomes during cell division in prokaryotes and eukaryotes. Two of the best studied SMC complexes are cohesin and condensin. Cohesin is required to hold sister chromatids together, which allows their bi-orientation on the mitotic spindle. Cleavage of cohesin’s kleisin subunit by the separase protease then triggers the movement of chromatids into opposite halves of the cell. Condensin is required to organize mitotic chromosomes into coherent structures to avoid that they get tangled up during segregation. Here we describe the discovery of SMC complexes and discuss recent advances in the understanding how this ancient protein family may function at a mechanistic level to fulfill its manifold roles in chromosome chemistry.