Fanconi anemia (also known as Fanconi anemia complementation group D2 (FANCD2)) is a 166 kD member of Fanconi anemia complementation group D. There are multiple isoforms of this nuclear protein including a post-translationally modified form. Activated FANCD2 co-localizes with BRCA1 in ionizing radiation-induced foci and in synaptonemal complexes of meiotic chromosomes. This protein is critical for cellular resistance to DNA cross-linking and cell-cycle arrest after ionizing radiation. DNA damage leads to monoubiquitination of FANCD2 and targeting to nuclear foci. Monoubiquitination occurs during normal cell cycle progression and is required for RAD51 and BRCA1 binding. This protein forms a complex with Fanconi proteins A, C, F, and G. FANCD2 has also been shown to bind to BRCA1, NBS1, and RAD51. The Poly6180 antibody recognizes the phosphorylated human FANCD2 protein (Ser222) and has been shown to be useful for Western blotting.