E3 ubiquitin-protein ligase that acts as a repressor of photomorphogenesis and as an activator of etiolation in darkness. E3 ubiquitin ligases accept ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates. Represses photomorphogenesis in darkness by mediating ubiquitination and subsequent proteasomal degradation of light-induced transcription factors such as HY5, HYH and LAF1. Down-regulates MYB21, probably via ubiquitination process. Light stimuli abrogate the repression of photomorphogenesis, possibly due to its localization to the cytoplasm. Could play a role in switching between skotomorphogenetic and photomorphogenetic pathways. Mediates the ubiquitination-dependent degradation of HY5 in the darkness during seedling development (e.g. hypocotyl growth) (PubMed:26474641). Represses CIP7 in darkness (PubMed:9668129). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Homodimer. Interacts with HY5, HYH, BBX24/STO, BBX25/STH, CIP8, COP10, SPA1, SPA2, SPA3, SPA4 and UVR8 and phosphorylated PHYA. Light induces dissociation of the SPA1/COP1 complex. Interacts with HRT/RPP8 and triggers it to the 26s proteasome. Binds to CRY2; this competitive interaction prevents triggering to proteasome of other binding proteins (PubMed:20624951). Binds to SHW1 in the nucleus (PubMed:26474641). Bonds to CIP7 (PubMed:9668129). Interacts with CSU2 (PubMed:26714275). Binds to CIP1 (PubMed:7753789). Interacts directly with DHU1 (PubMed:28735869). Localizes to the nucleus in darkness but is gradually relocated to the cytoplasm upon illumination. Localizes to subnuclear foci (speckle) and in dispersed nuclear localization in the dark. The coiled-coil domain (134-201) is necessary for SPA1, SPA3 or SPA4 binding. The DWD box is required for interaction with DDB1A. Autoubiquitinated. Abrogated induction of DHU1 in response to UV-B (PubMed:28735869). The double mutant shw1 cop1 displays an enhanced photomorphogenic growth in the darkness as well as abnormal accumulation of HY5 (PubMed:26474641). The double mutant dhu1-1 cop1-6 phenotype resemble that of the single mutant cop1-6 (PubMed:28735869). Plants lacking COP1 are not viable. Although plants lack TRIB proteins, a human TRIB1 peptide binds to a highly conserved surface on the top face of the beta propeller, indicating a general mode for recognition of peptide motifs by COP1.