Updated project metadata. The DNA damage response (DDR) is orchestrated by multiple, tightly regulated signalling events. We discovered that genetic suppressor element 1 (GSE1) forms a complex with the histone deacetylation 1 (HDAC1) / CoREST complex and that loss of GSE1 hampers DDR induction. To investigate how GSE1 and HDAC1 can regulate DDR and whether their mode of action might be overlapping, we performed a proteomic analysis using quantitative mass spectrometry based on the TMTpro 16-plex isobaric labelling technology (Li et al., 2020). We determined global acetylome and phosphorylome profiles in the nearly haploid human cell line HAP1 (Andersson et al, 1987) using WT, GSE1 KO and HDAC1 CI backgrounds and compared patterns between untreated and etoposide-treated (0.1 µM, 6 hrs) cells.