May act as a substrate-specific adapter of an E3 ubiquitin-protein ligase complex (CUL3-RBX1-BTB) which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (By similarity). Signal transducer of the phototropic response and photo-induced movements. Involved in the phot1 pathway under low blue light (LBL) fluence rate and in the phot2 pathway under higher fluence rate of blue light (HBL). Necessary for root and hypocotyl phototropisms, but not for the regulation of stomata opening. Not involved in chloroplast accumulation and translocation. Protein modification; protein ubiquitination. Interacts with PKS1, PKS2, RPT2, PHOT1 and PHOT2 (PubMed:10542152, PubMed:15031408, PubMed:16777956, PubMed:20071603). Subunit of a complex made of CAR6, PHOT1 and RPT3/NPH3 (PubMed:21367967). Expressed in hypocotyls, guard cells and mesophyll cells. In the root, up-regulated by red light. The BTB/POZ domain mediates the interaction with some component of ubiquitin ligase complexes. Phosphorylated in the dark. Impaired leaf flattening and slight epinasty when grown under blue light. May be due to an intron retention. Belongs to the NPH3 family.