Modification of tRNALysUUU by Elongator Is Essential for Efficient Translation of Stress mRNAs

Jorge Fernández-Vázquez,Damien Hermand,Miriam Sansó,Elena Hidalgo,Karin Buhne,Esther Paulo,Sebastian Leidel,Miguel Rodríguez-Gabriel,Itzel Vargas-Pérez,Mercè Carmona,José Ayté,Hiten D Madhani

doi:10.1371/journal.pgen.1003647

Jorge Fernández-Vázquez, Damien Hermand + Show 10 more

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https://doi.org/10.1371/journal.pgen.1003647

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Abstract

The Elongator complex, including the histone acetyl transferase Sin3/Elp3, was isolated as an RNA polymerase II-interacting complex, and cells deficient in Elongator subunits display transcriptional defects. However, it has also been shown that Elongator mediates the modification of some tRNAs, modulating translation efficiency. We show here that the fission yeast Sin3/Elp3 is important for oxidative stress survival. The stress transcriptional program, governed by the Sty1-Atf1-Pcr1 pathway, is affected in mutant cells, but not severely. On the contrary, cells lacking Sin3/Elp3 cannot modify the uridine wobble nucleoside of certain tRNAs, and other tRNA modifying activities such as Ctu1-Ctu2 are also essential for normal tolerance to H2O2. In particular, a plasmid over-expressing the tRNALys UUU complements the stress-related phenotypes of Sin3/Elp3 mutant cells. We have determined that the main H2O2-dependent genes, including those coding for the transcription factors Atf1 and Pcr1, are highly expressed mRNAs containing a biased number of lysine-coding codons AAA versus AAG. Thus, their mRNAs are poorly translated after stress in cells lacking Sin3/Elp3 or Ctu2, whereas a mutated atf1 transcript with AAA-to-AAG lysine codons is efficiently translated in all strain backgrounds. Our study demonstrates that the lack of a functional Elongator complex results in stress phenotypes due to its contribution to tRNA modification and subsequent translation inefficiency of certain stress-induced, highly expressed mRNAs. These results suggest that the transcriptional defects of these strain backgrounds may be a secondary consequence of the deficient expression of a transcription factor, Atf1-Pcr1, and other components of the transcriptional machinery.

Highlights

Unicellular organisms are exposed to the environment, and the major changes in microbial gene expression programs arise as a consequence of extracellular stresses
Transcription and mRNA homeostasis and translation have to be performed with maximum efficiency, or survival would be hampered
Our study demonstrates that the role of Elongator, a putative polymerase II (Pol II)-associated complex, in survival to stress is to optimize translation efficiency by modifying some particular transfer RNA (tRNA)

Summary

Introduction

Unicellular organisms are exposed to the environment, and the major changes in microbial gene expression programs arise as a consequence of extracellular stresses. The classical large complexes which contribute to a strong and efficient RNA polymerase II (Pol II) gene transcription, such as Mediator and SAGA, do contribute to stress survival, and genetic defects in non-essential components of these complexes can render phenotypes of sensitivity to stress. The MAP kinase Sty pathway is essential to induce massive changes in the gene expression programs in response to environment insults (for reviews, see [1,2]). Hundreds of genes become repressed, while hundreds of others are activated, to promote survival These genes, positively or negatively controlled by different stresses in a Sty1-dependent manner, were called CESR (core environmental stress response) genes [3]. The absence of the histone acetyl transferase (HAT) and SAGA component Gcn renders cells sensitive to several stresses due to defective chromatin remodelling along the stress genes [6,7]

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