Chromatin Remodeling and the Control of Gene Expression*

Biochemical and genetic findings accumulated over the past decade have established that the condensation of eukaryotic DNA in chromatin functions not only to constrain the genome within the boundaries of the cell nucleus but also to suppress gene activity in a general manner. This genetic repression extends from the level of the nucleosome, the primary unit of chromatin organization, where coiling of DNA on the surface of the nucleosome core particle impedes access to the transcriptional apparatus, to the higher order folding of nucleosome arrays and the organization of silent regions of chromatin (for reviews see Refs. 1–6 and 105). Chromatin structure is inextricably linked to transcriptional regulation, and recent studies show how chromatin is perturbed so as to facilitate transcription (for reviews see Refs. 7–12). Here, we review the substantial advances in the identification of histone acetyltransferases and histone deacetylases, whose opposing activities establish the steady-state level of histone acetylation, and progress in studies of multicomponent systems that require energy for the process of nucleosome disruption.