Chromatin is a complex of DNA and histone proteins that regulates gene expression as well as packaging genetic material to fit inside the cell. The proper functioning of chromatin also necessitates a web of interactions between molecular complexes that alter chromatin shape and organization to change DNA accessibility to transcription factors, resulting in the activation or repression of target DNA locus. Chromatin is divided into three types based on its shape and compaction state: euchromatin, heterochromatin, and centromeric chromatin. Euchromatin is characterized by active genes, broader spacing between nucleosomes, greater accessibility to transcription machinery, and histone modifications and variations that favor active transcription (reviewed in 34203193).
Morrison O, Thakur J. Molecular Complexes at Euchromatin, Heterochromatin and Centromeric Chromatin. Int J Mol Sci. 2021 Jun 28;22(13):6922. doi: 10.3390/ijms22136922. PMID: 34203193; PMCID: PMC8268097.