Trm112 Is Required for Bud23-Mediated Methylation of the 18S rRNA at Position G1575

Abstract

Posttranscriptional and posttranslational modification of macromolecules is known to fine-tune their functions. Trm112 is unique, acting as an activator of both tRNA and protein methyltransferases. Here we report that in Saccharomyces cerevisiae, Trm112 is required for efficient ribosome synthesis and progression through mitosis. Trm112 copurifies with pre-rRNAs and with multiple ribosome synthesis trans-acting factors, including the 18S rRNA methyltransferase Bud23. Consistent with the known mechanisms of activation of methyltransferases by Trm112, we found that Trm112 interacts directly with Bud23 in vitro and that it is required for its stability in vivo. Consequently, trm112Δ cells are deficient for Bud23-mediated 18S rRNA methylation at position G1575 and for small ribosome subunit formation. Bud23 failure to bind nascent preribosomes activates a nucleolar surveillance pathway involving the TRAMP complexes, leading to preribosome degradation. Trm112 is thus active in rRNA, tRNA, and translation factor modification, ideally placing it at the interface between ribosome synthesis and function.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.06623-11.

ACKNOWLEDGMENTS

We are indebted to E. Hurt (University of Heidelberg) for plasmids expressing Rps2-GFP and Rpl25-GFP (pRS316-Rps2p-eGFP and pRS316-RPL25-eGFP) and to B. Séraphin (CNRS, Strasbourg, France) for plasmid pBS1762. We thank Jaunius Urbonavicius (CMMI, Gosselies, Charleroi, Belgium) for suggesting to us the use of an alternative mapping strategy to detect the m⁷G1575 modification. We are grateful to Stéphanie Kervestin and Marc Dreyfus (IBPC, Paris, France) for critical reading of the manuscript.

Work in the lab of V.H.-H. was supported by the Agence Nationale pour la Recherche (grant ANR-07-JCJC-0105) and the CNRS. During this work, S.F. held a predoctoral grant from the Université Pierre et Marie Curie. Work in the lab of D.L.J.L. was funded by the FRIA, the FRS-FNRS, the Communauté Française de Belgique (ARC), and the Région Wallone (Cibles). M.G. is indebted to the CNRS, the Université Paris-Sud 11, and the Human Frontier Science Program (grant number RGP0018/2009-C) for financial support.