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Translocation of proteins across the endoplasmic reticulum. III. Signal recognition protein (SRP) causes signal sequence-dependent and site-specific arrest of chain elongation that is released by microsomal membranes

By Peter Walter and Gonter Blobel


ABSTRACT Translocation-competent microsomal membrane vesicles of dog pancreas were shown to selectively bind nascent, in vitro assembled polysomes synthesizing secretory protein (bovine prolactin) but not those synthesizing cytoplasmic protein (alpha and beta chain of rabbit globin). This selective polysome binding capacity was abolished when the microsomal vesicles were salt-extracted but was restored by an 11S protein (SRP, Signal Recognition Protein) previously purified from the saltextract of microsomal vesicles (Walter and Blobel, 1980. Proc. Nat /. Acad. Sci. U. S. A. 77:7112-7116). SRP-dependent polysome recognition and binding to the microsomal membrane was shown to be a prerequisite for chain translocation. Modification of SRP by N-ethyl maleimide abolished its ability to mediate nascent polysome binding to the microsomal vesicles. Likewise, polysome binding to the microsomal membrane was largely abolished when 8-hydroxy leucine, a Leu analogue, was incorporated into nascent secretory polypeptides. The data in this and the preceding paper provide conclusive experimental evidence that chain translocation across the endoplasmic reticulum membrane is a receptor-mediated event and thus rule out proposals that chain translocation occurs spontaneously and without the mediation by proteins. Moreover, our data here demonstrate conclusively that the initial events that lead to translocatio

Year: 1981
DOI identifier: 10.1083/jcb.91.2.557
OAI identifier: oai:CiteSeerX.psu:
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