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. 2015 Feb 18;11(11):1330–1334. doi: 10.1080/15476286.2014.996457

Figure 1.

Figure 1.

SRP mediated co-translational protein targeting. (A) Scheme of human SRP bound to the ribosome – nascent chain complex (RNC). The S domain recognizes the signal at the ribosomal tunnel exit and the Alu domain binds to the factor binding site (FBS) causing “elongation arrest." (B) RNA gymnastics in SRP S domain assembly. SRP19 (pdb code 3ktv (42) and SRP68-RBD (4p3e (22); and remainder of SRP68/72) are attached in the nucleolus, while the functional particle with SRP54 (1qzw; structure from an archaeal complex57) is completed in the cytosol. (C) SRP RNA remodeling of helix 5 and the 5f-loop (orange) by the insertion of an ARM motif (brown) of SRP68-RBD. (D) The assembled SRP S domain bound to the RNC.20 The signal is recognized by SRP54-M (open conformation) and SRP54-NG is flipped to the apex of the particle. The opened SRP RNA 5f-loop is in contact with rRNA.