Protection from proteasomal degradation of Epo-R^S462A. BaF3 cells expressing either Epo-R^WT or Epo-R^S462A were preincubated with LLnL (L) or methylamine (M) for 15 minutes and stimulated for 30 minutes with¹²⁵I-Epo. After washing to remove unbound radioactivity, the cells were lysed, and clarified cell extracts were crosslinked with 2 mM of BS3. Excess crosslinking reagent was blocked with ethanolamine, and Epo-R was precipitated with a polyclonal antibody directed against the intracellular domain of the receptor (C-236). Precipitates were denatured by boiling in sodium dodecyl sulfate and subsequently immunoprecipitated again with the same antibody (left panel). Lastly, nonprecipitated¹²⁵I-Epo-crosslinked proteins were recovered by immunoprecipitation with anti-Epo antibodies (right panel). Experiment analysis was performed by polyacrylamide gel electrophoresis and autoradiography.