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Vol. 19, Issue 12, 5279-5288, December 2008

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Ribosome-associated Complex Binds to Ribosomes in Close Proximity of Rpl31 at the Exit of the Polypeptide Tunnel in Yeast

Kristin Peisker^*,,, Daniel Braun^*,, Tina Wölfle^*,, Jendrik Hentschel^*,, Ursula Fünfschilling, Gunter Fischer, Albert Sickmann^||, and Sabine Rospert^*,

*Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, D-79104 Freiburg, Germany; Centre for Biological Signalling Studies (BIOSS), University of Freiburg, D-79104 Freiburg, Germany; Fakultät für Biologie, University of Freiburg, D-79104 Freiburg, Germany; Max Planck Research Unit for Enzymology of Protein Folding, D-06120 Halle/Saale, Germany; ^||Department of Proteomics, Institute for Analytical Sciences, D-44139 Dortmund, Germany

Submitted June 30, 2008; Revised August 19, 2008; Accepted September 24, 2008
Monitoring Editor: Jonathan S. Weissman

Ribosome-associated complex (RAC) consists of the Hsp40 homolog Zuo1 and the Hsp70 homolog Ssz1. The chaperone participates in the biogenesis of newly synthesized polypeptides. Here we have identified yeast Rpl31, a component of the large ribosomal subunit, as a contact point of RAC at the polypeptide tunnel exit. Rpl31 is encoded by RPL31a and RPL31b, two closely related genes. rpl31arpl31b displayed slow growth and sensitivity to low as well as high temperatures. In addition, rpl31arpl31b was highly sensitive toward aminoglycoside antibiotics and suffered from defects in translational fidelity. With the exception of sensitivity at elevated temperature, the phenotype resembled yeast strains lacking one of the RAC subunits or Rpl39, another protein localized at the tunnel exit. Defects of rpl31arpl31bzuo1 did not exceed that of rpl31arpl31b or zuo1. However, the combined deletion of RPL31a, RPL31b, and RPL39 was lethal. Moreover, RPL39 was a multicopy suppressor, whereas overexpression of RAC failed to rescue growth defects of rpl31arpl31b. The findings are consistent with a model in that Rpl31 and Rpl39 independently affect a common ribosome function, whereas Rpl31 and RAC are functionally interdependent. Rpl31, while not essential for binding of RAC to the ribosome, might be involved in proper function of the chaperone complex.

Address correspondence to: Sabine Rospert (sabine.rospert{at}biochemie.uni-freiburg.de)

Abbreviations used: NAC, nascent polypeptide associated complex; RAC, ribosome-associated complex; 31-ribosomes, ribosomes isolated from a rpl31arpl31b strain; 39-ribosomes, ribosomes isolated from a rpl39 strain; RPB, ribosome-associated protein biogenesis factors; SRP, signal recognition particle.