Substrate recognition component of a SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of target proteins. Recognizes and binds to phosphorylated target proteins. Directs ubiquitination of the phosphorylated CDK inhibitor SIC1. Involved in the degradation of CDC6 together with CDC34/UBC3 and CDC53, and in restricting the degradation of FAR1 to the nucleus. Is essential for initiation of DNA replication and separation of the spindle pole bodies to form the poles of the mitotic spindle. It also plays a role in bud development, fusion of zygotic nuclei after conjugation and various aspects of sporulation. Required for HTA1-HTB1 locus transcription activation. Required for G1/S and G2/M transition. Protein modification; protein ubiquitination. Interacts with DCD53 and SKP1. Component of the SCF(CDC4) complex containing CDC53, SKP1, RBX1 and CDC4. CDC34. Interacts with CDC6 and CIC1. Interacts with SIC1; the interaction involves a SIC1 double phosphorylated motif (degron). Homodimerizes; the dimerization increases SIC1 ubiquitination in vitro.