| Abstract: |
Gene expression can be regulated at the level of initiation of protein biosynthesis via structural elements present at the 5′ untranslated region of mRNAs. These folded mRNA segments may bind to the ribosome, thus blocking translation until the mRNA unfolds. Here, we report a series of cryo-electron microscopy snapshots of ribosomal complexes directly visualizing either the mRNA structure blocked by repressor protein S15 or the unfolded, active mRNA. In the stalled state, the folded mRNA prevents the start codon from reaching the peptidyl-tRNA (P) site inside the ribosome. Upon repressor release, the mRNA unfolds and moves into the mRNA channel allowing translation initiation. A comparative structure and sequence analysis suggests the existence of a universal stand-by site on the ribosome (the 30S platform) dedicated for binding regulatory 5′ mRNA elements. Different types of mRNA structures may be accommodated during translation preinitiation and regulate gene expression by transiently stalling the ribosome. © 2007 Elsevier Inc. All rights reserved. |
| Keywords: |
unclassified drug; sequence analysis; mutation; nonhuman; protein conformation; image analysis; protein binding; time factors; rna; gene expression regulation; amino acid sequence; molecular sequence data; sequence homology, amino acid; messenger rna; protein synthesis; rna, messenger; 5' untranslated region; escherichia coli; base sequence; models, molecular; binding sites; nucleic acid conformation; codon; rna structure; transfer rna; rna, transfer; sequence homology, nucleic acid; repressor protein; regulatory rna sequence; reaction analysis; ribosomal proteins; escherichia coli proteins; gene expression regulation, bacterial; structural homology, protein; ribosomes; regulatory sequences, ribonucleic acid; 5' untranslated regions; rna, bacterial; cryoelectron microscopy; ribosome; translation regulation; peptide chain initiation, translational; peptide transfer ribonucleic acid; repressor protein s15
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