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. Protein modification; protein ubiquitination. A number of isoforms are produced. According to EST sequences. The BTB/POZ domain mediates the interaction with some component of ubiquitin ligase complexes. Belongs to the NPH3 family.