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). Involved in repression of deetiolation in the developing seedling. Repression of photomorphogenesis is probably mediated by ubiquitination and subsequent degradation of photomorphogenesis-promoting factors such as HY5, HYH and LAF1. Involved in the repression of blue light responsive promoter in chloroplasts. May be required to stabilize the CDD complex. Its association with histone tail suggests a role in remodeling of chromatin (PubMed:9681024, PubMed:15342494). Required for the regulation of histone H2B monoubiquitination (H2Bub) over most genes by controlling the stability of the deubiquitination module (DUB module) (PubMed:30192741). Component of the CDD complex, at least composed of COP10, DET1 and DDB1A (PubMed:15342494, PubMed:24563205). Interacts with DDB1A (PubMed:12225661). Interacts with non-acetylated N-terminal tail of histone H2B in a nucleosome context (PubMed:12225670). Displays a rather patchy distribution forming a punctuated pattern in the euchromatin (PubMed:30192741). Does not localize in the heterochromatic chromocenters or nucleolus (PubMed:30192741). Belongs to the DET1 family.