A role for Gcn5 in heterochromatin structure, gene silencing and NER at theHMLlocus in budding yeast

Histone acetyltransferase Gcn5 plays an important role in transcription activation, DNA replication-coupled nucleosome assembly and nucleotide excision repair (NER). However, its functions on the heterochromatin are unexplored. Here, we find that removal of Gcn5 leads to more condensed heterochromatin structure, as revealed by topology analysis of HML circles. Importantly, the altered heterochromatin structure is restored by re-expression of Gcn5 in the gcn5Δ cells. As a result of the more compact heterochromatin, gene silencing at the HML locus is increased and NER efficiency at HML is impaired in the absence of Gcn5. Interestingly, while the association of SIR complex with HML is enhanced in cells lacking Gcn5, the altered compaction of HML heterochromatin is also observed due to the deletion of Gcn5 from Sir − cells. These findings reveal a role of Gcn5 in the regulation of heterochromatin structure, gene silencing and NER efficiency at the heterochromatic HML locus in yeast.