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Primary Citation Related Structures:  5MDV, 5MDW, 5MDY, 5MDZ
PubMed Abstract: 
Ribosomes stall when they encounter the end of messenger RNA (mRNA) without an in-frame stop codon. In bacteria, these "nonstop" complexes can be rescued by alternative ribosome-rescue factor A (ArfA). We used electron cryomicroscopy to determine structures of ArfA bound to the ribosome with 3'-truncated mRNA, at resolutions ranging from 3.0 to 3.4 angstroms. ArfA binds within the ribosomal mRNA channel and substitutes for the absent stop codon in the A site by specifically recruiting release factor 2 (RF2), initially in a compact preaccommodated state. A similar conformation of RF2 may occur on stop codons, suggesting a general mechanism for release-factor-mediated translational termination in which a conformational switch leads to peptide release only when the appropriate signal is present in the A site.
Organizational Affiliation: 
Medical Research Council (MRC) Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Medical Research Council (MRC) Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK. ramak@mrc-lmb.cam.ac.uk.