Protein complexes that modify chromatin

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Initially, eukaryotic chromosomes were viewed as static structures that merely stored inactive DNA, with the belief that packaging DNA into chromatin was sufficient to repress gene expression. The primary distinction between eukaryotic and prokaryotic genomes was thought to be this extensive packaging, with both types regulated similarly by cis-acting sequences and trans-acting factors. However, our understanding of eukaryotic chromosomes has significantly changed over the past decade. They are now seen as dynamic organelles that actively regulate genetic information flow. Chromatin's fluidity means that even the maintenance of gene quiescence is an active and tightly regulated process. This dynamism arises from protein complexes that modify histones, remove modifications, and manage nucleosome stability and mobility. Numerous such complexes have been identified, with some being abundant and playing global roles in chromosome function, while others are rare and specialized for specific tasks at particular loci. Many of these complexes exhibit overlapping functions and share biochemical activities. Their components have been uncovered through genetic screens, as well as innovative cell biological and biochemical methods.