MCB130lectures6,7 - MCB130 R. Schekman Membrane Assembly:...

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MCB130 Lectures 6, 7 R. Schekman Membrane Assembly: Signal Hypothesis and Translocation Machinery A. Signal hypothesis 1. Proteins destined for secretion or assembly in plasma membrane originate on ribosomes attached to endoplasmic reticulum (ER). a. Isolated complex shows nascent chains attached to ribosomes and partly embedded in ER membrane. b. Addition of components required for completion of protein chains allows proteins to be transported into ER vesicle. 2. Synthesis of secretory protein precursors in a reticulocyte lysate. a. Immunoglobulin light chain made with NH 3 + terminal 2K dalton prepeptide. b. In vitro transport coupled to synthesis when ER vesicles present during translation. c. Signal peptide cleaved during transport into ER by signal peptidase on the inner surface of the membrane. B. Cytoplasmic and membrane proteins required for translocation 1. Biochemical fractionation has revealed two components required for early events in transport. a.
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MCB130lectures6,7 - MCB130 R. Schekman Membrane Assembly:...

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