Chromatin remodelling

Chromatin can be altered by various post-translational modifications to its histone proteins to allow differential access to DNA: this is chromatin remodelling. Some chromosome regions are highly condensed, forming transcriptionally inactive heterochromatin. Others regions (euchromatin) are decondensed and potentially transcriptionally active. Chromatin remodelling is required for transcription, replication, repair, and recombination to occur. It is achieved by acetylation, phosphorylation, or methylation of histone tails extruding from nucleosomes. Acetylated histones are associated with regions of open chromatin, allowing access to transcriptional machinery. Histone acetyltransferases (HATs) acetylate histone tails, and histone deacetylases (HDACs) deacetylate them.