Mechanism of ribosome rescue by ArfA and RF2.

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eLife, ISSN: 2050-084X, Vol: 6

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10.7554/elife.23687; 10.7554/elife.23687.016; 10.7554/elife.23687.015; 10.7554/elife.23687.014; 10.7554/elife.23687.002; 10.7554/elife.23687.009; 10.7554/elife.23687.013; 10.7554/elife.23687.001; 10.7554/elife.23687.008; 10.7554/elife.23687.026; 10.7554/elife.23687.025
Demo, Gabriel; Svidritskiy, Egor; Madireddy, Rohini; Diaz-Avalos, Ruben; Grant, Timothy; Grigorieff, Nikolaus; Sousa, Duncan; Korostelev, Andrei A.
eLife Sciences Publications, Ltd; eLife Sciences Organisation, Ltd.
Neuroscience; Biochemistry, Genetics and Molecular Biology; Immunology and Microbiology; ArfA; E. coli; biochemistry; biophysics; release factor 2; ribosome rescue; stalled ribosome; stop-codon-independent termination; structural biology; Biophysics; Structural Biology
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article description
ArfA rescues ribosomes stalled on truncated mRNAs by recruiting release factor RF2, which normally binds stop codons to catalyze peptide release. We report two 3.2 Å resolution cryo-EM structures - determined from a single sample - of the 70S ribosome with ArfA•RF2 in the A site. In both states, the ArfA C-terminus occupies the mRNA tunnel downstream of the A site. One state contains a compact inactive RF2 conformation. Ordering of the ArfA N-terminus in the second state rearranges RF2 into an extended conformation that docks the catalytic GGQ motif into the peptidyl-transferase center. Our work thus reveals the structural dynamics of ribosome rescue. The structures demonstrate how ArfA 'senses' the vacant mRNA tunnel and activates RF2 to mediate peptide release without a stop codon, allowing stalled ribosomes to be recycled.