ATP-dependent chromatin remodeling activities

Genetic and biochemical approaches have indicated that the packaging of DNA into chromatin can be repressive to transcription [1]. ATP-dependent chrom atin remodelling activities can facilitate transcription from chromatin tem plates [2]. Consistent with this, biochemical assays have shown that the ac tion of ATP-dependent chromatin remodelling activities increase the accessi bility of DNA within chromatin templates [3]. However more recent functiona l studies suggest that many ATP-dependent chromatin remodelling activities can also function as repressors of transcription. Here we review recent adv ances to our understanding of the biological function of these complexes. W e then consider some of the mechanisms by which ATP-dependent chromatin rem odelling activities together with other forms of chromatin remodelling or m odifying enzymes may act to regulate genomic accessibility either positivel y or negatively.