Mechanisms for ATP-dependent chromatin remodelling

Gene regulation involves the generation of a local chromatin topology that is conducive to transcription. Several classes of chromatin remodelling act ivity hare been shown to play a role in this process. ATP -dependent chroma tin- remodelling activities use energy derived from the hydrolgsis of ATP t o alter the structure of chromatin, making it more accessible for transcrip tion factor binding. The yeast SWI-SWF complex is the founding member of th is family of ATP-dependent chromatin-remodelling activities. We have develo ped a model system to study the ability of the SWI-SWF complex to alter chr omatin structure. Using this system, we find that SWI-SWF is able to alter the position of nucleosomes along the DNA. This is consistent with recent r eports that other ATP-dependent chromatin-remodelling activities can alter the positions of nucleosomes along DNA. This suggests that nucleosome mobil ization may be a general feature of the activity of ATP-dependent chromatin -remodelling activities. Some of the mechanisms by which nucleosomes may be moved along DNA are discussed.