 Although the individual parts vary, all cullin-based ubiquitin ligases exhibit these characteristics.The DDB1 adaptor protein was initially characterized as the large subunit of a heterodimeric complex (UV-DDB) that was found to recognize damaged DNA and participate in a form of repair known as nucleotide excision repair (NER).The smaller subunit of this Damaged DNA Binding protein complex is known as DDB2 and is able to directly bind DNA lesions associated with UV-irradiation.