Component of light signal transduction machinery. Involved in repression of photomorphogenesis in darkness by participating in the CDD complex, a complex probably required to regulate the activity of ubiquitin conjugating enzymes (E2s). Repression of photomorphogenesis is probably mediated by ubiquitination and subsequent degradation of photomorphogenesis-promoting factors such as HY5, HYH and LAF1. Plays a role in DNA repair by forming with DDB2 the UV-damaged DNA-binding protein complex (UV-DDB). Component of the CUL4-RBX1-DDB1-PRL1 E3 ubiquitin-protein ligase complex. Protein modification; protein ubiquitination. Component of the CDD complex, at least composed of COP10, DET1 and DDB1A (PubMed:15342494, PubMed:24563205). Component of the CUL4-RBX1-CDD complex (PubMed:16844902). Component of the CUL4-RBX1-DDB1-PRL1 E3 ubiquitin-protein ligase complex (PubMed:18223036). Component of the UV-DDB complex, which is composed of DDB1A and DDB2 (PubMed:17409070). Interacts with RAE1 (PubMed:16844902, PubMed:18223036). Interacts with WDR55 (PubMed:22447688). Interacts with ATCSA-1 (PubMed:20128879). Interacts with DDA1 (PubMed:24563205). Binds to ASG2; the subcellular localization of this complex depends on ASG2 farnesylation status (PubMed:26147561). Binds to KTN80.2/DWA3 (PubMed:21421380). Interacts with HTD1 (PubMed:25358503). Interacts directly with DHU1 (PubMed:25193399). Translocates to the nucleus upon exposure to UV (PubMed:18551167). Excluded from the nucleus when in complex with farnesylated ASG2 (PubMed:26147561). A number of isoforms are produced. According to EST sequences. Belongs to the DDB1 family.