heterochromatin formation facultative heterochromatin formation https://github.com/geneontology/go-ontology/issues/22325 https://github.com/geneontology/go-ontology/issues/23553 2021-10-29T13:40:47Z GO:0140718 fHC assembly Note that facultative heterochromatin can be reprogrammed, as opposed to constitutive heterochromatin which usually cannot be reprogrammed to a transcriptionally-competent state. Note also that facultative heterochromatin formation does not usually involve DNA methylation, while constitutive heterochromatin formation does. pg biological_process facultative heterochromatin assembly The compaction of chromatin into a conformation that is refractory to transcription but that can be converted to euchromatin and allow transcription in specific contexts. These can be temporal (e.g., developmental states or specific cell-cycle stages), spatial (e.g., nuclear localization changes from the center to the periphery or vice versa due to exogenous factors/signals), or parental/heritable (e.g., monoallelic gene expression). In metazoa, this involves the methylation of histone H3K27, and in certain cases methylation of H3K9. On the other hand, in unicellular eukaryotes, only methylation of H3K9 is involved and H3K27 is not methylated.