FIG. 3.

(A) Characterization of carbohydrates attached to M by digestion with glycosidases. Immunoprecipitated lysates (I) and supernatants (E) of M-expressing cells either were left untreated or were treated with the indicated enzymes. Digestions with PNGase F and O-glycosidase were performed on denatured proteins, according to the instructions of the manufacturers. (B) Glycosylation and secretion of mutant MΔ27-47, devoid of the proposed O glycan attachment site. Immunoprecipitated lysate (I) and supernatant (E) of transfected and labeled cells either were left untreated (lanes 1 and 2) or were digested with PNGase F (lane 3). Nonglycosylated (p) and glycosylated (gp or ggp) forms of wild-type and mutant M and internally initiated S are indicated to the left of each panel.