Schematic of human F-box proteins with functional domains, arranged into subclasses FBXL, FBXO, and FBXW series. F: F-box motif; L: Leucine-rich repeats; Hr: Hemerythrin-like domain; JmjC: Jomonji C domain; CXXC: CXXC-type Zing finger; PHD: PHD-type Zing finger; Cyclin N: Cyclin N-terminal domain; Cyclin C: Cyclin C-terminal domain; PEST: proline (P), glutamic acid (E), serine (S), and threonine (T) sequence; IBR: In between RING fingers domain; Ub: Ubiquitin-like domain; PI31 N: Proteasome regulator, N-terminal domain; TPR: Tetratricopeptide repeat β: Parallel β-helix repeat; NosD: Parallel β-helix domain found in Periplasmic copper-binding protein; UBR: Ubiquitin protein ligase E component n-recognin; UD: UvrD-like helicase N-terminal domain; UvrDC: UvrD-like helicase C-terminal domain; K: Kelch repeat; FBA: F-box associated domain; SPRY: SPLA and the ryanodine receptor domain; D: D Domain of β-TRCP; WD: WD40 repeat.