F-box proteins have been shown to be critical for the ubiquitin-mediated degradation of cellular regulatory proteins, and they are a family of eukaryotic proteins characterized by an approximately 40 amino acid motif. SCF complex, a class of ubiquitin ligases, consists of invariable components, Skp1 and Cullin, and variable components of F-box proteins, which have a primary role in determining substrate specificity. The F-box proteins are divided into 3 classes: FBWs containing WD-40 domains, FBLs containing leucine-rich repeats, and FBXs containing either different protein-protein interaction modules or no recognizable motifs. FBOX9 has three isoforms produced by alternative splicing with predicted MW of 38-42, 47 and 50-60 kDa.