An active chromatin sequence (ACS) is a region of DNA in a eukaryotic chromosome in which histone modifications such as acetylation lead to exposure of the DNA sequence thus allowing binding of transcription factors and transcription to take place. Active chromatin may also be called euchromatin. ACSs may occur in non-expressed gene regions which are assumed to be "poised" for transcription. The sequence once exposed often contains a promoter to begin transcription. At this site acetylation or methylation can take place causing a conformational change to the chromatin. At the active chromatin sequence site deacetylation can cause the gene to be repressed if not being expressed.
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- Sabo PJ, Humbert R, Hawrylycz M, et al. (March 2004). "Genome-wide identification of DNaseI hypersensitive sites using active chromatin sequence libraries". Proc. Natl. Acad. Sci. U.S.A. 101 (13): 4537–42. Bibcode:2004PNAS..101.4537S. doi:10.1073/pnas.0400678101. PMC 384782. PMID 15070753.
- Roh TY, Cuddapah S, Zhao K (2005). "Active chromatin domains are defined by acetylation islands revealed by genome-wide mapping". Genes Dev. 19 (5): 542–52. doi:10.1101/gad.1272505. PMC 551575. PMID 15706033.