Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex. May play a role in accumulation of expanded polyglutamine (polyQ) protein huntingtin (HTT) (By similarity). Protein modification; protein ubiquitination. Part of a SCF (SKP1-cullin-F-box) protein ligase complex consisting of FBXO25, SKP1, CUL1 and RBX1. Interacts directly with SKP1 and CUL1 (By similarity). Interacts (via C-terminus) with actin (via N-terminus) (By similarity). In the nucleus, associates with a specific and novel subnuclear dot-like structure. The F-box is necessary for the interaction with SKP1.