Bilder Forschung
Heterochromatin boundary formation by ‘chromatin sculpting’. (A) The anti-silencing protein Epe1 is uniformly recruited to heterochromatin through binding to Heterochromatin Protein 1 (HP1), which recognizes methylated lysine 9 of histone H3 (H3K9me), a conserved histone mark of heterochromatin. (B) Inside heterochromatin, Epe1 is selectively modified with ubiquitin (‘ubiquitylation’) by the E3 ubiquitin ligase Cul4-Ddb1-Cdt2, which marks Epe1 for degradation by the proteasome. (C). At the heterochromatin boundaries, Epe1 is protected by an unknown mechanism from ubiquitylation and degradation, resulting in its local accumulation. Epe1 at the heterochromatin boundary prevents further spreading of H3K9me-marked heterochromatin. This ‘sculpting’ mechanism explains how Epe1 can acts as a boundary factor while it is prevented from interfering with heterochromatin inside the domain.
