eukromatin

Euchromatin, also spelled eukromatin in some sources, is a form of chromatin that is relatively decondensed during interphase and enriched for active genes. It contrasts with heterochromatin, which is more condensed and largely transcriptionally silent. In euchromatin, DNA is accessible to transcription factors, RNA polymerase II, and other components of the transcriptional machinery, enabling gene expression.

Molecularly, euchromatin is associated with histone modifications that favor transcription, such as acetylation of histone tails (for example H3K9ac, H3K27ac) and activating marks like H3K4me3 at promoters and H3K36me3 along gene bodies. Nucleosome remodeling complexes such as SWI/SNF and ISWI help to maintain an open chromatin state. Euchromatin tends to be located in the interior of the nucleus and is often in early-replicating regions of the genome.

Euchromatin is dynamic and can transition to a more repressed state during development or in response to signals, converting to facultative or constitutive heterochromatin marked by repressive histone marks (for example H3K9me3, H3K27me3) and DNA methylation. Overall, the open conformation of euchromatin supports gene-rich transcriptional activity, while the more condensed heterochromatin is associated with gene silencing and structural roles.