Minimal essential medium chain

The role of catalysis in membrane assembly is emphasized again by the above model since the N-terminal sequence of the nascent polypeptide chain of a spanning protein is released by proteolysis as soon as it reaches the cytosol. The N-terminal polypeptide chain extension may help the chain penetrate the hydrophobic bilayer and solubilize the resulting hydrophobic N-terminal part of the chain in the aqueous medium of the cytoplasm. However, the role of the protease-catalyzed hydrolysis of the polypeptide chain in membrane assembly is minimized in the membrane trigger hypothesis (99). According to this model, the essential role of the leader sequence would be to modify, in association with the lipid bilayer, the folding pathway of the protein in such a way that the polypeptide chain could span the membrane. 

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