Chromatin reassembly signals the end of DNA repair

The packaging of the eukaryotic genome into chromatin provides a formidable obstacle to the machinery that mediates genomic processes such as transcription, repair and replication. The cell solves this accessibility problem during double-strand DNA repair by removing the histone proteins flanking the DNA lesion. Presumably then, the repaired DNA is subsequently reassembled into chromatin in order to allow the epigenetic information to be restored and to repackage and protect the genome. Our recent work has shown that chromatin is indeed reassembled following double-strand break repair in budding yeast. Furthermore, the assembly of the repaired DNA into chromatin is driven by acetylation within the globular domain of histone H3, on lysine 56 (H3 K56Ac). Unexpectedly, we also discovered that H3 K56Ac and chromatin assembly onto the repaired DNA is essential to turn off the DNA damage cell cycle checkpoint. This work demonstrates that reformation of the chromatin structure, not DNA repair per se, is the elusive signal that tells the cell when DNA repair is complete.