Our biochemical data revealed a novel BRCA1 transcriptional target—RRM2. Further investigations suggested that the BRCA1-regulated RRM2 expression in GBM cells was dependent on E2F1, a transcriptional factor previously reported as transcriptional activator of RRM2 (refs 30, 33) (Fig. 4c,e). Here, E2F1 is linked to glioblastoma.