fig1

Figure 1. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) in balance - physiologic vs. pathologic. In physiologic state, HAT enzymes and HDAC enzymes work in tandem to regulate gene transcription. HATs induce an open chromatin conformation (favoring gene transcription), which is counterbalanced by the action of HDACs that induce a closed chromatin conformation (favoring gene silencing). In pathologic state (e.g., neoplastic change) this balanced is tipped, favoring either an unregulated open chromatin conformation or an unregulated closed chromatin conformation. Schematically shown is an instance of an unregulated closed chromatin conformation due to a pathologic increase in HDAC enzymes. This unregulated, pathologic state may silence physiologic regulatory pathways in the cell, such as those protein products that regulate the cell cycle genes (e.g., tumor suppressor genes)