fig2

Figure 2. Histone modification of Histone acetylases and Histone deacetylases. Chromatin is in a closed conformation when acetylation groups are removed from histones by HDACs, thereby preventing access to key TF. Acetylases attach ac to histones, which contributes to a more open chromatin conformation that allows transcription factors to bind to DNA (bottom). HATs and HDACs also target numerous non-histone substrates, including transcription factors (e.g., p53), chaperones (e.g., Hsp90) and signaling molecules (e.g., NF-κB). The balance between the activities of HATs and HDACs serves as a critical regulatory mechanism for gene expression.