Fig. 4. Membrane requirements for R4op and Ii insertion into PKRM. R4op and Ii were synthesised in the RRL. Membranes washed in high-salt buffer supplemented with puromycin (PKRM), mock-treated (PKRM mock) or treated with 1 or 2 µg/ml trypsin (PKRM-T 1 and PKRM-T 2, respectively) were present during the synthesis of Ii. R4op was incubated with these membranes post-translationally. Where indicated, 100 nM of soluble SRP receptor (SR) was added. Proteins were analysed by SDS-PAGE and autoradiography. Ii^*, nonglycosylated Ii; g-R4op, glycosylated R4op.