DDB1 and xeroderma pigmentosum: We find that bXAB2 interacts with the DNA damage-binding protein-1 (DDB1) involved in UV-induced DNA damage recognition34, and with a portion of xeroderma pigmentosum, complementation group A protein (XPA) known to assemble the NER incision complex at sites of DNA damage35, in control and UV-irradiated cells (Fig. S1B).