Abstract
Many protein complexes that drive key processes in cells are “molecular motors”—assemblies that consume (electro)chemical energy to produce mechanical work. Examples include the FoF1 synthase rotary motor that catalyzes adenosine triphosphate (ATP) production, kinesin and myosin motors that “walk” along cytoskeleton filaments, or polymerases and helicases that move along DNA. Structural-maintenance of chromosomes protein complexes (SMCs) have only recently been identified as an entirely distinct class of DNA-translocating motors, although their key role in folding the linear DNA double helix into intricate three-dimensional structures, such as X-shaped mitotic chromosomes, was known for decades. Here, we discuss how insights from biophysical, biochemical, and structural studies are starting to yield an understanding of the mechanism by which these motors extrude loops of DNA to structure genomes.