UV-B specific signaling component that acts as UV-B photoreceptor and plays a key role in establishing UV-protective responses in plants. Upon UV-B irradiation, UVR8 undergoes an immediate switch from homodimer to monomer, accumulates in the nucleus, interacts with the photomorphogenic repressor COP1 and regulates the expression of the transcription factor HY5 by associating with chromatin (through histone H2B binding) in the HY5 promoter region. UVR8 is involved in controlling aspects of leaf growth and morphogenesis in response to UV-B, is required for normal progression of endocycle and has a regulatory role in stomatal differentiation. Is required for plant circadian clock response to photomorphogenic UV-B light, partly through the transcriptional activation of responsive clock genes. Promotes photosynthetic efficiency at elevated levels of UV-B. Plays a role in mediating the effects of UV-B radiation on pathogen resistance by controlling the expression of the sinapate biosynthetic pathway. The two tryptophans, Trp-285 and Trp-233, serve collectively as the UV-B chromophore. Homodimer in the absence of UV-B, but absorption of UV-B induces monomerization of UVR8 and interaction with COP1. Interacts with RUP1, RUP2 and histone H2B. UV-B promotes rapid accumulation of UVR8 in the nucleus. Hypersensitivity to ultraviolet-B (UV-B) illumination (PubMed:12226503, PubMed:28735869). Abrogated induction of DHU1 in response to UV-B (PubMed:28735869). Disruption in a plant lacking DHU1 alleviates its hypersensitivity to UV-B (PubMed:28735869).