FIGURE 7.

EndoH sensitivity of U21 is unchanged when folded class I molecules are unavailable. U21-expressing or U21 + shβ₂m (β₂m kd) U373 astrocytoma cells were pulsed with [³⁵S]methionine for 15 min and chased for the indicated times. Immunoprecipitates (IP) with either anti-U21 (a) or W6/32 (b) were divided, and half of the recovered material was treated with endoglycosidase H, as noted. U21 and class I heavy chains (HC) are noted, as are migration of EndoH-sensitive and EndoH-resistant forms of U21. Of note, EndoH-sensitive U21, which loses four N-linked glycans, migrates slightly more slowly than EndoH-sensitive class I MHC, so that the two bands are indistinguishable from one another (lanes 4). The double asterisk in b denotes a possible contaminating cross-reactive polypeptide (visible in lanes 5, 7, 8, 10, and 11). c, U21-expressing U373 or K562 cells were pulsed and chased and treated with EndoH as described above. U21, class I MHC heavy chains, and their EndoH-sensitive and -resistant counterparts are noted.