Essential component of the SCF (SKP1-CUL1-F-box protein) ubiquitin ligase complex, which mediates the ubiquitination of proteins involved in cell cycle progression, signal transduction and transcription. In the SCF complex, serves as an adapter that links the F-box protein to CUL1 (By similarity). Protein modification; protein ubiquitination. Interacts directly with CUL1 and F-box proteins, such as BTRC and SKP2, in the SCF complex (By similarity). Interacts with mtus1. May interact with fbx28, fbxo43, fbl5 and fbl13. Belongs to the SKP1 family.