Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex. Isoform 3 regulates neural transmission by binding and ubiquitinating RIMS1, a modulator of presynaptic plasticity. Interacts with SKP1 and CUL1. Isoform 3 is present at the presynaptic membrane. Highly expressed in brain. Altered electrophysiological synaptic activity, with increased frequency of miniature excitatory postsynaptic currents. Intron retention.