Component of a cullin-RING-based BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex that mediates the ubiquitination and subsequent proteasomal degradation of target proteins, but with relatively low efficiency. Cullin-RING-based BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complexes containing homodimeric SPOPL or the heterodimer formed by SPOP and SPOPL are less efficient than ubiquitin ligase complexes containing only SPOP. May function to down-regulate the activity of cullin-RING-based BCR (BTB-CUL3-RBX1) E3 ubiquitin- protein ligase complexes that contain SPOP. . This is the function of SPOPL (speckle type BTB/POZ protein like, Ensembl gene identifier ENSG00000144228).