ATP-dependent chromatin remodeling factors: Nucleosome shufflers with manymissions

This review addresses recent developments in the field of ATP-dependent chr omatin remodeling factors. These factors use the energy of ATP hydrolysis t o introduce superhelical torsion into DNA, which suggests a common mechanis tic basis of action. Chromatin remodeling factors function both in transcri ptional activation and repression, but they may hale roles outside of trans criptional regulation such as DNA repair. A study of the nucleosome depende nt ATPase ISWI in yeast illustrates the involvement of ATP-dependent chroma tin remodeling in transcriptional repression by setting up inaccessible chr omatin structures at promoters. However, factors such as ISWI are also invo lved in the restructuring of large chromatin domains and even whole chromos omes. Transcriptional regulation by ATP-dependent chromatin remodeling fact ors occurs in concert with histone modifying enzymes such as histone acetyl transferases and histone deacetylases: In yeast, SWI/SNF targeting is a req uirement for histone acetyltransferases activity at promoters that are acti ve at late stages of mitosis, when the chromatin is still condensed, This d emonstrates that ATP-dependent remodeling factors facilitate covalent histo ne modifications. However, they are also regulated by histone modifications and in some circumstances they function in parallel with histone modificat ions towards the same goal.