Ribosome rescue pathways recycle stalled ribosomes and target problematic mRNAs and aborted proteins for degradation 1,2 . In bacteria, it remains unclear how rescue pathways distinguish ribosomes stalled in the middle of a transcript from actively translating ribosomes 3-6 . Here, using a genetic screen in Escherichia coli, we discovered a new rescue factor that has endonuclease activity. SmrB cleaves mRNAs upstream of stalled ribosomes, allowing the ribosome rescue factor tmRNA (which acts on truncated mRNAs 3 ) to rescue upstream ribosomes. SmrB is recruited to ribosomes and is activated by collisions. Cryo-electron microscopy structures of collided disomes from E. coli and Bacillus subtilis show distinct and conserved arrangements of individual ribosomes and the composite SmrB-binding site. These findings reveal the underlying mechanisms by which ribosome collisions trigger ribosome rescue in bacteria.
Organizational Affiliation:
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, USA.
Gene Center and Department of Biochemistry, University of Munich, Munich, Germany.
Computational Biology Branch, National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, USA.
Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, USA.
Gene Center and Department of Biochemistry, University of Munich, Munich, Germany. beckmann@genzentrum.lmu.de.
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, USA. buskirk@jhmi.edu.
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