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. Abolished brassinosteroid (BR)-induced ASK7/BIN2/SK21 degradation, and BR-insensitivity. Suppression of the constitutive BR-response phenotype in the dominant mutant bzr1-1D, and accumulation of phosphorylated BZR1.