A complex containing βTrCP recruits Ccd34 to catalyse ubiquitination of IκBα

AbstractActivation of transcription factor NF-κB is accomplished by degradation of its inhibitor IκBα. Signal induced phosphorylation of IκBα on serine 32 and 36 targets the protein for ubiquitination on lysine 21 and 22. Here we use a phosphorylated peptide substrate representing residues 20–43 of IκBα to investigate requirements for ubiquitination of IκBα. Phosphorylation dependent polyubiquitination is carried out by a multiprotein complex containing βTrCP, Skp1 and Cdc53 (Cul1). In the presence of ubiquitin activating enzyme and the protein complex containing βTrCP, polyubiquitination of IκBα peptide was dependent on the presence of Cdc34, while Ubc5 only stimulated mono- and di-ubiquitination