Component of E3 ubiquitin ligase complexes. Required for normal neuromuscular synaptogenesis, axon pathfinding and neuronal migration (By similarity). Plays a role in the regulation of neurotransmission at mature neurons (By similarity). May control synaptic activity by controlling UNC13A via ubiquitin dependent pathway (By similarity). Specifically recognizes TP73, promoting its ubiquitination and degradation. Protein modification; protein ubiquitination. Forms a complex with MYCBP2 and SKP1 but does not appear to form an authentic SCF (SKP1-CUL1-F-box protein) complex (By similarity). Interacts (via B30.2/SPRY domain) with TP73 (via SAM domain); leading to TP73 ubiquitination and degradation by proteasome. Interacts (via SRY domain) with UNC13A; leading to degradation of UNC13A by the proteasome (By similarity). Down-regulated in response to DNA-damage. Belongs to the FBXO45/Fsn family.