translocation of the amino terminus of the protein into the ER membrane lumen. This translocation, which has been demonstrated with opsin with in vitro experiments, breaks the usual pattern of "co-translational" translocation which has always held for mammalian proteins targeted to the ER. A great deal of the mechanics of transmembrane topology and folding remains to be elucidated.

Post-translational translocation

Even though most secretory proteins are co-translationally translocated, some are

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