Key assembly factor of SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase complexes that promotes the exchange of the substrate-recognition F-box subunit in SCF complexes, thereby playing a key role in the cellular repertoire of SCF complexes. Acts as a F-box protein exchange factor (By similarity). Required for SCF(TIR1) function. Modulates SCF(TIR1) function through its interactions with the CUL1 subunit. Represses photomorphogenesis by promoting HY5 degradation in darkness. Interacts with CUL1 and CUL4. Binds unneddylated CUL1, but cannot bind CUL1 once it has been neddylated. Highly expressed in roots. Expressed in stems, flowers and siliques. Developmental phenotypes such as dwarfism, organ defects, short inflorescences and mishaped leaves. Low fertility and reduced responses to hormones. Belongs to the CAND family.