Heterochromatin assembly: fix definition

[pgaudet]

Change from "The assembly of chromatin into heterochromatin, a compact and highly condensed form that is often, but not always, transcriptionally silent." to ~"The assembly of chromatin into heterochromatin, resulting in a chromatin conformation refractory to transcription. This process starts with heterochromatin nucleation, spreading, and ends with heterochromatin boundary formation.~

• add references PMID: 25192661 PMID:33827924 (nucleation)

[pgaudet]

• move directly under chromatin assembly (ie, remove chromatin remodeling parent)

[pgaudet]

Fix definition AGAIN An epigenetic gene regulation mechanism that involves the assembly of chromatin into heterochromatin, resulting in a chromatin conformation refractory to transcription. This process starts with heterochromatin nucleation, its spreading, and ends with heterochromatin boundary formation.

to represent the is_a parent, 'negative regulation of gene expression, epigenetic'