Fig. 6. Opsin TM3 exit from the ER translocon is independent of subsequent TM domains. OPTM1-3PPL was constructed by replacing the region of opsin located on the C-terminal side of TM3 with hydrophilic sequence derived from preprolactin. Membrane associated integration intermediates of 164 and 204 residues with a single cysteine probe located in TM3 (residue 115, cf. Fig. 5A) were then subjected to BMH-dependent crosslinking and the resulting adducts recovered by immunoprecipitation and analysed by SDS-PAGE. All symbols are as previously defined.