English: Recombinational repair of DNA double-strand damage - some key steps. ATM (ATM) is a protein kinase that is recruited and activated by DNA double-strand breaks. DNA double-strand damages also activate the Fanconi anemia core complex (FANCA/B/C/E/F/G/L/M).^[1] The FA core complex monoubiquitinates the downstream targets FANCD2 and FANCI.^[2] ATM activates (phosphorylates) CHEK2 and FANCD2.^[3] CHEK2 phosphorylates BRCA1.^[4] Ubiquinated FANCD2 complexes with BRCA1 and RAD51.^[5] The PALB2 protein acts as a hub,^[6] bringing together BRCA1, BRCA2 and RAD51 at the site of a DNA double-strand break, and also binds to RAD51C, a member of the RAD51 paralog complex RAD51B-RAD51C-RAD51D-XRCC2 (BCDX2). The BCDX2 complex is responsible for RAD51 recruitment or stabilization at damage sites.^[7] RAD51 plays a major role in homologous recombinational repair of DNA during double strand break repair. In this process, an ATP dependent DNA strand exchange takes place in which a single strand invades base-paired strands of homologous DNA molecules. RAD51 is involved in the search for homology and strand pairing stages of the process.