Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Histone deacetylase 5 is an enzyme that in humans is encoded by the HDAC5 gene.Histones play a critical role in transcriptional regulation, cell cycle progression, and developmental events. Histone acetylation/deacetylation alters chromosome structure and affects transcription factor access to DNA. The protein encoded by this gene belongs to the class II histone deacetylase/acuc/apha family.