Clearing of ribosome collisions by the ribosome quality control trigger complex RQT

After translational stalls, colliding eukaryotic ribosomes are cleared through dissociation into subunits by the ribosome quality control trigger complex, RQT, by an unknown mechanism. Here we show that RQT requires accessible mRNA and the presence of a neighboring ribosome. Cryo-EM of several RQT-ribosome complexes revealed the structural basis of splitting: RQT engages the 40S subunit of the lead ribosome and can switch between two conformations. We propose a mechanistic model in which the Slh1 helicase subunit of RQT applies a pulling force on the mRNA, causing destabilizing conformational changes of the 40S subunit. The collided ribosome functions as a ram or giant wedge, ultimately resulting in subunit dissociation. Our findings provide a first conceptual framework for a helicase driven ribosomal splitting mechanism.One-Sentence SummaryRQT clears collided ribosomes by pulling mRNA to trigger destabilizing conformational transitions for subunit dissociation.