Abstract
Genetic and biochemical approaches have indicated that the packaging of DNA into chromatin can be repressive to transcription. ATP-dependent chromatin remodelling activities can facilitate transcription from chromatin templates. Consistent with this, biochemical assays have shown that the action of ATP-dependent chromatin remodelling activities increase the accessibility of DNA within chromatin templates. However more recent functional studies suggest that many ATP-dependent chromatin remodelling activities can also function as repressors of transcription. Here we review recent advances to our understanding of the biological function of these complexes. We then consider some of the mechanisms by which ATP-dependent chromatin remodelling activities together with other forms of chromatin remodelling or modifying enzymes may act to regulate genomic accessibility either positively or negatively.