ATP-dependent chromatin-remodelling complexes seem to have evolved to accommodate the major changes in chromatin regulation that occurred during the evolution of vertebrates from unicellular eukaryotes (Box 1). As an example, complexes of the SWI/SNF family, which is one of the most-studied families of chromatin-remodelling complexes, have lost, gained and shuffled subunits during evolution from yeast to vertebrates. In particular, the transition to vertebrate chromatin-remodelling complexes involved the expansion of several of the gene families encoding the subunits and the use of combinatorial assembly, which together are predicted to allow the formation of several hundred complexes. But what is the advantage of combinatorial assembly?
