a, HEK 293T cells were transfected with Rpr, GST alone or GST—Rpr and FLAG-tagged XIAP protein. Proteins were precipitated with anti-FLAG or anti-Rpr antibodies and blotted with anti-FLAG. Proteins were precipitated with glutathione—Sepharose or anti-FLAG, and detected by immunoblotting with anti-GST or anti-FLAG. Although GST—Rpr and XIAP failed to coprecipitate, the untagged Rpr control clearly coprecipitated with XIAP protein. b, A pulse-chase experiment was performed as in Fig. 1c, using either wild-type Rpr (Rpr) or untagged Rpr lacking its first 15 amino acids (Rpr16-–65). The results were then quantified.