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. 1995 Nov 15;14(22):5485–5493. doi: 10.1002/j.1460-2075.1995.tb00235.x

A complex of the signal sequence binding protein and the SRP RNA promotes translocation of nascent proteins.

S Hauser 1, G Bacher 1, B Dobberstein 1, H Lütcke 1
PMCID: PMC394662  PMID: 8521805

Abstract

Translocation of proteins across the endoplasmic reticulum membrane is initiated by the signal recognition particle (SRP), a cytoplasmic ribonucleoprotein complex consisting of a 7S RNA and six polypeptides. To investigate the functions of the SRP components, we have tested the activities of several SRP subparticles. We show that the SRP GTPase (SRP54) alone binds a signal sequence and discriminates it from a non-signal sequence. Although SRP54 alone is unable to promote translocation, SRP54 in a complex with SRP RNA is both necessary and sufficient to promote translocation of an elongation-arrested nascent protein in a GTP-regulated manner. For co-translational translocation, additional SRP components are required. We discuss the implications of our results for the function of the Escherichia coli SRP which is homologous to the SRP54/SRP-RNA complex.

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