TPRKB enhances TP53RK binding to IMiDs. (A) TP53RK, TPRKB, or both were overexpressed in HEK293FT cells using c-Myc–tagged expression vectors. Whole cell lysates were subjected to Pom-bead pull-down assay and silver staining (top panel) or western blot using an infrared imaging system (bottom panel). (B) TPRKB was knocked down in H929 cells. STD, saturation-transfer difference. (C) Len binding to TP53RK in the presence of TPRKB. Binding of Len to TP53RK was assessed by NMR spectrometry in the presence or absence of TPRKB.