Before mammalian genomes were sequenced and genome-wide analyses of chromatin function became possible, ATP-dependent chromatin remodelling was thought to be largely a permissive mechanism that operates to allow the binding of general transcription factors. However, the discovery that a large number of non-redundant genes are involved in chromatin remodelling and the ability to carry out more rigorous genetic analyses is enabling the specialized and instructive functions of these complexes to be defined. These functions arise partly from the combinatorial assembly of the complexes. The assembly of complexes from products of gene families suggest that biological specificity is produced in much the same way that letters produce meaning by being assembled into words. But the mechanisms by which these chromatin-remodelling ‘words’ are ‘translated’ into specific biological functions are still unclear, and new ways to probe complex chromatin structure might be needed before we can improve our mechanistic understanding. This is particularly true of BAF complexes, which can regulate transcription from significant distances from promoters and therefore cannot be accurately studied using the available in vitro assays.
