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Nat Struct Mol Biol. 2016 Nov;23(11):1003-1010. doi: 10.1038/nsmb.3299. Epub 2016 Sep 26.

Dual interaction of the Hsp70 J-protein cochaperone Zuotin with the 40S and 60S ribosomal subunits.

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Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, USA.


Ribosome-associated J protein-Hsp70 chaperones promote nascent-polypeptide folding and normal translational fidelity. The J protein Zuo1 is known to span the ribosomal subunits, but understanding of its function is limited. Here we present new structural and cross-linking data allowing more precise positioning of Saccharomyces cerevisiae Zuo1 near the 60S polypeptide-exit site and suggesting interactions of Zuo1 with the ribosomal protein eL31 and 25S rRNA helix 24. The junction between the 60S-interacting and subunit-spanning helices is a hinge that positions Zuo1 on the 40S yet accommodates subunit rotation. Interaction between the Zuo1 C terminus and 40S occurs via 18S rRNA expansion segment 12 (ES12) of helix 44, which originates at the decoding site. Deletions in either ES12 or the Zuo1 C terminus alter readthrough of stop codons and -1 frameshifting. Our study offers insight into how this cotranslational chaperone system may monitor decoding-site activity and nascent-polypeptide transit, thereby coordinating protein translation and folding.

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