Substrate recognition component of a SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complex that mediates the ubiquitination and subsequent proteasomal degradation of target proteins. Promotes ubiquitination of CCND1 and its subsequent proteasomal degradation. Recognizes TERF1 and promotes its ubiquitination together with UBE2D1 (By similarity). Protein modification; protein ubiquitination. Homodimer. Directly interacts with SKP1 and CUL1. Part of the SCF (SKP1-CUL1-F-box) E3 ubiquitin-protein ligase complex SCF(FBXO4) formed of CUL1, SKP1, RBX1 and FBXO4. Interacts with TERF1; this interaction is prevented in the presence of GNL3L. Identified in a complex with CRYAB and CCND1 (By similarity). Phosphorylation at Ser-11 varies during the cell cycle. It is low in resting cells and high in the S phase and the G2/M phase of the cell cycle. Phosphorylation is decreased during late G1 phase. Phosphorylation at Ser-11 is important for homodimerization and for optimal ubiquitin ligase activity towards CCND1 (By similarity).