Component of SCF(ASK-cullin-F-box) E3 ubiquitin ligase complexes, which may mediate the ubiquitination and subsequent proteasomal degradation of target proteins. Required for brassinosteroid (BR) signal transduction. Mediates ASK7/BIN2/SK21 inactivation both by competing with substrate binding (e.g. BZR1) and by promoting its ubiquitination and subsequent proteasomal degradation. Part of a SCF (SKP1-cullin-F-box) protein ligase complex. Binds directly to several GSK3 family proteins such as SKP1A/ASK1, ASK1/SK11, ASK3/SK12, ASK5/SK13, ASK7/BIN2/SK21, ASK9/SK22 and ASK6/SK23. Interacts with ASK7/BIN2/SK21 in a brassinosteroid (BR)-dependent manner. Mostly localized in the nucleolus, and, to a lower extent, in the cytoplasm. Expressed in seedlings, leaves, stems, flower buds and flowers. Abolished brassinosteroid (BR)-induced ASK7/BIN2/SK21 degradation, and severe BR-insensitivity. Suppression of the constitutive BR-response phenotype in the dominant mutant bzr1-1D, and accumulation of phosphorylated BZR1.