Identification of a novel 300-kDa factor termed IκBαE3-F1 that is required for ubiquitinylation of IκBα

AbstractDestruction of IκB by ubiquitinylation is required for signal-dependent activation of NF-κB. The IκBα ubiquitin-ligase activity associated with phosphorylated IκBα (pIκBα) in HeLa cells was almost completely lost by washing under stringent conditions including 1 M NaCl; nevertheless, an SCFβTrCP complex containing Skp1, Cullin-1, and F-box/WD40 protein βTrCP was still bound to pIκBα, suggesting the existence of a putative factor that is loosely associated with pIκBα and may collaborate with SCFβTrCP. The factor was named IκBαE3-F1 and was partially purified from HeLa cells. Gel filtration analysis revealed that IκBαE3-F1 has an apparent molecular mass of approximately 300 kDa