The DM-deficient cell line, 9.5.3, its wild-type progenitor, 8.1.6, and 9.5.3 cells transfected with DM (9.5.3-DM) were pulse-labeled for 1 hr with [35S]-Cys/Met and chased for 0, 2, or 8 hrs. NP-40 cell extracts (3×106 cell equivalents/lane) were immunoprecipitated with the anti-DR mAb L243 and analyzed by 12% SDS-PAGE. The positions of DR α and β chains and of a 10 kDa SLIP fragment of Ii are indicated. Levels of DR-associated CLIP are substantially diminished in DM-expressing 8.1.6 cells at 2 hr and 8 hr of chase, and even further reduced when DM levels are increased by DM transfection of 9.5.3 cells. Also note inefficient IP of immature DR (mostly Ii-associated) in pulse-labeled cells with L243, which accounts for the weak bands at 0 hr chase [53].