Cell
Volume 164, Issues 1–2, 14 January 2016, Pages 91-102
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Article
Insertion of the Biogenesis Factor Rei1 Probes the Ribosomal Tunnel during 60S Maturation

https://doi.org/10.1016/j.cell.2015.11.027Get rights and content
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Highlights

  • Cryo-EM structure of the 60S-Arx1-Alb1-Rei1 complex at 3.4 Å resolution

  • Rei1 inserts a C-terminal segment deeply into the polypeptide tunnel

  • Cytoplasmic 60S maturation is precluded when Rei1 insertion into the tunnel fails

  • The structure reveals elements of Arx1 responsible for binding near the tunnel exit

Summary

Eukaryotic ribosome biogenesis depends on several hundred assembly factors to produce functional 40S and 60S ribosomal subunits. The final phase of 60S subunit biogenesis is cytoplasmic maturation, which includes the proofreading of functional centers of the 60S subunit and the release of several ribosome biogenesis factors. We report the cryo-electron microscopy (cryo-EM) structure of the yeast 60S subunit in complex with the biogenesis factors Rei1, Arx1, and Alb1 at 3.4 Å resolution. In addition to the network of interactions formed by Alb1, the structure reveals a mechanism for ensuring the integrity of the ribosomal polypeptide exit tunnel. Arx1 probes the entire set of inner-ring proteins surrounding the tunnel exit, and the C terminus of Rei1 is deeply inserted into the ribosomal tunnel, where it forms specific contacts along almost its entire length. We provide genetic and biochemical evidence that failure to insert the C terminus of Rei1 precludes subsequent steps of 60S maturation.

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Present address: California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA 94720-3220, USA