SRP RNA Remodeling by SRP68 Explains Its Role in Protein Translocation

Abstract

Dissecting SRP In the secretory pathway, inserting transmembrane and secretory proteins into and through hydrophobic cell membranes is facilitated by a highly conserved RNA and protein-containing molecular machine, the signal recognition particle (SRP). Grotwinkel et al. (p. 101 ) determined the x-ray crystal structures of human SRP RNA (7SL RNA) bound to the RNA-binding domain (RBD) of the protein SRP subunit SRP68, both in the presence and absence of the SRP19 subunit. The 7SL RNA is remodeled by the SRP68-RBD, which bends one domain of the RNA and remodels a loop, exposing two nucleotides, which allow direct interaction with the ribosome. The findings explain how the SRP RNA drives translation elongation arrest, which is required for membrane insertion.