Transfer RNA Maturation Defects Lead to Inhibition of ribosomal RNA Processing via Synthesis of pppGpp

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Mechanism of activation of methyltransferases involved in translation by the Trm112 ‘hub’ protein

Methylation is a common modification encountered in DNA, RNA and proteins. It plays a central role in gene expression, protein function and mRNA translation. Prokaryotic and eukaryotic class I translation termination factors are methylated on the glutamine of the essential and universally conserved GGQ motif, in line with an important cellular role. In eukaryotes, this modification is performed by the Mtq2-Trm112 holoenzyme. Trm112 activates not only the Mtq2 catalytic subunit but also two other tRNA methyltransferases (Trm9 and Trm11). To understand the molecular mechanisms underlying methyltransferase activation by Trm112, we have determined the 3D structure of the Mtq2-Trm112 complex and mapped its active site. Using site-directed mutagenesis and in vivo functional experiments, we show that this structure can also serve as a model for the Trm9-Trm112 complex, supporting our hypothesis that Trm112 uses a common strategy to activate these three methyltransferases

The essential nature of YqfG, a YbeY homologue required for 3′ maturation of Bacillus subtilis 16S ribosomal RNA is suppressed by deletion of RNase R

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Rae1/YacP, a new endoribonuclease involved in ribosome-dependent mRNA decay in Bacillus subtilis

The PIN domain plays a central role in cellular RNA biology and is involved in processes as diverse as rRNA maturation, mRNA decay and telomerase function. Here, we solve the crystal structure of the Rae1 (YacP) protein of Bacillus subtilis, a founding member of the NYN (Nedd4-BP1/YacP nuclease) subfamily of PIN domain proteins, and identify potential substrates in vivo. Unexpectedly, degradation of a characterised target mRNA was completely dependent on both its translation and reading frame. We provide evidence that Rae1 associates with the B. subtilis ribosome and cleaves between specific codons of this mRNA in vivo. Critically, we also demonstrate translation-dependent Rae1 cleavage of this substrate in a purified translation assay in vitro. Multiple lines of evidence converge to suggest that Rae1 is an A-site endoribonuclease. We present a docking model of Rae1 bound to the B. subtilis ribosomal A-site that is consistent with this hypothesis and show that Rae1 cleaves optimally immediately upstream of a lysine codon (AAA or AAG) in vivo

The catalytic activity of the translation termination factor methyltransferase Mtq2-Trm112 complex is required for large ribosomal subunit biogenesis

International audienceThe Mtq2-Trm112 methyltransferase modifies the eukaryotic translation termination factor eRF1 on the glutamine side chain of a universally conserved GGQ motif that is essential for release of newly synthesized peptides. Although this modification is found in the three domains of life, its exact role in eukaryotes remains unknown. As the deletion of MTQ2 leads to severe growth impairment in yeast, we have investigated its role further and tested its putative involvement in ribosome biogenesis. We found that Mtq2 is associated with nuclear 60S subunit precursors, and we demonstrate that its catalytic activity is required for nucleolar release of pre-60S and for efficient production of mature 5.8S and 25S rRNAs. Thus, we identify Mtq2 as a novel ribosome assembly factor important for large ribosomal subunit formation. We propose that Mtq2-Trm112 might modify eRF1 in the nucleus as part of a quality control mechanism aimed at proof-reading the peptidyl transferase center, where it will subsequently bind during translation termination