Figure 1.

A model for the change in nucleosome occupancy in a typical yeast gene in different transcriptional states. (a) When there is no transcription, repressor proteins bind to their DNA-binding sites and maintain a repressive chromatin configuration with nucleosomes all along the gene and most of the promoter. (b) When activator proteins bind their DNA elements, they promote changes in chromatin that disrupt or displace nucleosomes from promoter regions, leading to transcription of the gene. Subsequent transcript elongation through coding regions causes the transient displacement of histones. (c) With higher levels of transcription, nucleosomes become depleted from coding regions as well as from the promoter.