Fig. 5. Signal peptide cleavage of US11-180 is significantly delayed. (A) Processing of US11-215 and US11-180 was examined in stable transfectants of MG-U373 cells using pulse–chase analysis. US11 was recovered from SDS lysates using α-US11 serum and analyzed by SDS–PAGE (12.5%). The signal peptide-containing form of US11 (spUS11-215) and the mature processed form of US11 (mUS11-215) were immunoprecipitated from US11-215 cells (lanes 1–4). Two major species, ** and the mature processed form of US11-180 (mUS11-180), were recovered from US11-180 cells. (B) Half of the α-US11 precipitate recovered from a pulse–chase experiment of US11-180 cells was digested with Endo H (lanes 5–8). (C) The slower moving US11-180 polypeptide (**) was subjected to N-terminal radiosequencing. The radioactivity (c.p.m.) recovered at each Edman cycle is shown.