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bioRxiv · 10.1101/091256

Mechanism of ribosome rescue by ArfA and RF2

Demo, G.·Svidritskiy, E.·Madireddy, R.·Diaz-Avalos, R.·Grant, T.·Grigorieff, N.·Sousa, D.·Korostelev, A.
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Abstract

ArfA rescues ribosomes stalled on truncated mRNAs by recruiting the release factor RF2, which normally binds stop codons to catalyze peptide release. We report two 3.2-[A] 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, hitherto unobserved in 70S termination complexes. 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.

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Demo, G., Svidritskiy, E., Madireddy, R., Diaz-Avalos, R., Grant, T., Grigorieff, N., Sousa, D., Korostelev, A.. 2016-12-02. Mechanism of ribosome rescue by ArfA and RF2. https://doi.org/10.1101/091256

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