ASH1L methyltransferase deposits H3K4me3 and FACT for damage verification in nucleotide excision repair [ChIP-Seq ASH1L-CTD]
To recognize DNA damage, nucleotide excision repair (NER) deploys a multipart mechanism by which the XPC sensor detects helical distortions followed by engagement of TFIIH for lesion verification. Accessory players ensure that this factor handover takes place on chromatin where DNA is wrapped around histones. We show that the histone methyltransferase ASH1L, once activated by MRG15, accelerates global-genome NER activity. Upon UV irradiation, ASH1L deposits H3K4me3 marks all over the genome (except in gene promoters), thus priming chromatin for relocations of XPC from native to damaged DNA. ASH1L further recruits the histone chaperone FACT to UV lesions. In the absence of ASH1L, MRG15 or FACT, XPC persists on damaged DNA without being able to deliver lesions to the TFIIH verifier. We conclude that ASH1L implements repair hotspots whose H3K4me3 and FACT occupancy confers an active promoter-like code and organization of histones that make DNA damage verifiable by the NER machinery. Overall design: Chromatin immunoprecipitation sequencing (ChIP-seq) for histone mark H3K36me2 in wildtype U2OS cells and for ASH1L-CTD (or, as an input control, empty vector) transfected into ASH1L knockout U2OS cells. Wildtype and ASH1L knockout cells were either not exposed to UV or assayed 3 hours post UV.