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

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.

Genome-wide Screening of Regulators of Catalase Expression

“…The Elongator and Trm112 Complexes Are Revealed in the Genetic Screen-We recently reported that Elongator, a tRNA-modifying complex promoting efficient translation, was required for wild-type tolerance to peroxides (5). Indeed, our genetic screen also indicates that deletion of genes coding for different Elongator components express lower levels of basal or induced Ctt1-GFP (Table 2).…”

“…Thus, we recently described that mutations in Elongator components impair wild-type tolerance to peroxides, probably by decreasing the amount of proteins synthesized from the stress mRNAs (5). Elongator introduces a modification of the anticodon loop of the low copy number tRNA UUU Lys as well as in other two types of tRNAs with a uracil 34 (U 34 ) in the 5Ј position of the anticodon (6,7).…”

“…Elongator introduces a modification of the anticodon loop of the low copy number tRNA UUU Lys as well as in other two types of tRNAs with a uracil 34 (U 34 ) in the 5Ј position of the anticodon (6,7). Modification of tRNA UUU Lys by Elongator (introducing an acetyl group at position 5 of U 34 (cm 5 U 34 )) and by Ctu1-Ctu2 complex (catalyzing the thiolation at carbon 2 of U 34 (s 2 U 34 )) is required for the efficient recognition by this tRNA of the codon AAA and, therefore, for optimal performance under situations requiring a robust translation process, such as abrupt changes in the gene expression program during adaptation to stress (5).…”

A functional genome-wide genetic screening identifies new pathways controlling the G1/S transcriptional wave

“…We recently reported that the activity of this complex was required for proper tolerance to H 2 O 2 stress and that this effect was mediated by enhanced translation of the transcription factor Atf1. 19 From the 6 subunits of the Elongator complex, only Delp2 and Delp5 had wild type YFP/FSC ratios, with Diki3/Delp1 and Delp4 having the lowest YFP/FSC ratios (0.52) of all the strains that we tested from the knock-out collection, even below the strain lacking the known MBF co-activator Rep2 (0.55) (Fig. 3E and Table 1).…”

“…This fact was not completely surprising, since Trm112 dimerizes with another protein (either Trm9 or Mtq2) to form an active methylase that modifies specific nucleotides in tRNAs. 19 However, and despite these strains displaying decreased MBF activity (measured with the reporter strain or as the level of cdc18 transcript), none of these mutants were sensitive to hydroxyurea (HU) (Fig. 3C).…”