Activation and repression in the nervous system.

The mechanisms underlying transcriptional activation and repression have become much clearer. Recent evidence suggests that transcription factors that do not bind DNA directly, the co-activators and co-repressors, mediate a large number of cell signaling events. Their association with histone acetylases, to mediate activation, or deacetylases, to mediate repression, provide a model for explaining how gene expression is regulated.