| Pseudosubstrate regulation of the SCF ( beta TrCP ) ubiquitin ligase by hnRNP U . beta TrCP / E3RS ( E3RS ) is the F box protein that functions as the receptor subunit of the SCF ( beta TrCP ) ubiquitin ligase ( E 3 ) . ^^^ However , unlike pI ( kappa ) Balpha , which is targeted by SCF ( beta TrCP ) for degradation , the E 3 bound hnRNP U is stable and is , therefore , a pseudosubstrate . ^^^ Consequently , hnRNP U engages a highly neddylated active SCF ( beta TrCP ) , which dissociates in the presence of a high affinity substrate , resulting in ubiquitination of the latter . ^^^ |