 The C-terminal region of DDB2 (a 48 kDa molecular weight protein) is essential for binding to DDB1 (a larger 127 kDa protein).Together, the two proteins form a UV-damaged DNA binding protein complex (UV-DDB).If humans have a mutation in each copy of their "DDB2" gene, this causes a mild form of the human disease xeroderma pigmentosum, called XPE.