Fig. 4. CFTR degradation involves simultaneous loss of multiple epitopes. The schematic shows the topological structure of CFTR and relative locations of N-terminal (N), C-terminal (C) and regulatory (R) domain epitopes. NDB, nucleotide-binding domain; *, location of methionine residues; open circles, N-linked glycosylation sites. (A) Control CFTR degradation assay performed as in Fig. 1. (B-D) Degradation products from panel A were immunoprecipitated with peptide-specific antisera raised against the N-terminus (), C-terminus () or R-domain () epitopes. Fragments recovered with each antibody were quantified by scintillation counting and expressed as the percentage of counts recovered at t=0.