May act as a substrate receptor of a CUL4-RING E3 ubiquitin-protein ligase (CRL4) complex involved in the negative regulation of cellular responses to ultraviolet-B (UV-B) illumination, likely in coordination with RUP1 (PubMed:25193399, PubMed:28735869). Interacts with COP1 and probably prevents the formation of active UVR8-COP1 complex, thus avoiding UVR8-COP1-mediated positive regulation of UV-B responses (PubMed:28735869). Interacts directly with DDB1A (PubMed:25193399). Binds to COP1 and RUP1 (PubMed:28735869). Accumulates in response to ultraviolet-B (UV-B) illumination. Hypersensitivity to ultraviolet-B (UV-B) illumination leading to short hypocotyls under UV-B; the sensitivity to UV-B is alleviated by the disruption of UVR8 and requires the presence of COP1 and HY5 (PubMed:25193399, PubMed:28735869). The double mutants dhu1-1 cop1-6 and dhu1-1 hy5-215 phenotypes resemble that of single mutants cop1-6 and hy5-215, respectively (PubMed:28735869). The UV-B responsiveness of the double mutant dhu1-1 rup1-1 is similar to that of the single mutants dhu1-1 and rup1-1 (PubMed:28735869).