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, trm112⌬ 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.A ctively growing budding yeast cells produce an average of 33 ribosomes per second, which is considerable (61). Besides the synthesis of its constituents, i.e., 79 ribosomal proteins and 4 rRNAs, ribogenesis involves a large number of so-called transacting factors, including proteins and small nucleolar RNAs (13, 56). These interact only transiently with preribosomes and are required for pre-rRNA processing (i.e., cleavages), pre-rRNA modification, and preribosome assembly and transport.Ribosome synthesis is initiated in the nucleolus, a highly dynamic specialized subcompartment of the nucleus organized around clusters of actively transcribed rRNA genes (60). There, RNA polymerase I produces a 35S/47S (in yeasts and humans, respectively) primary transcript which is processed through a complex succession of endo-and exoribonucleolytic cleavages into three of the four mature rRNAs, the 18S, 5.8S, and 25S/28S rRNAs. The fourth rRNA, 5S, is independently transcribed by RNA polymerase III. Ribosome maturation starts cotranscriptionally in the nucleolus, progresses in the nucleoplasm until preribosomes reach the nuclear pore complex, and is finalized in the cytoplasm. Cytoplasmic maturation steps consisting of pre-rRNA processing and structural reorganization result in the assembly of prominent ribosomal structures, such as the "beak" of the small subunit (SSU) and the "stalk" of the large subunit, and are a prerequisite to the acquisition of functionality (43).It is not clear how the various facets of ribosome synthesis are integrated with ribosome function. However, there is growing evidence that such coordination exists. For the small subunit, recent cryoelectron microscopy (cryo-EM) maps of late pre-40S subunits indicate that the binding of trans-acting factors literally mask functional sites, preventing premature translation initiation (57). For the large subunit, trans-acting factors that resemble ribosomal proteins (suc...

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.

bThe genes encoding the ribonucleases RNase J1 and RNase Y have long been considered essential for Bacillus subtilis cell viability, even before there was concrete knowledge of their function as two of the most important enzymes for RNA turnover in this organism. Here we show that this characterization is incorrect and that ⌬rnjA and ⌬rny mutants are both viable. As expected, both strains grow relatively slowly, with doubling times in the hour range in rich medium. Knockout mutants have major defects in their sporulation and competence development programs. Both mutants are hypersensitive to a wide range of antibiotics and have dramatic alterations to their cell morphologies, suggestive of cell envelope defects. Indeed, RNase Y mutants are significantly smaller in diameter than wild-type strains and have a very disordered peptidoglycan layer. Strains lacking RNase J1 form long filaments in tight spirals, reminiscent of mutants of the actin-like proteins (Mre) involved in cell shape determination. Finally, we combined the rnjA and rny mutations with mutations in other components of the degradation machinery and show that many of these strains are also viable. The implications for the two known RNA degradation pathways of B. subtilis are discussed. Defining the full set of essential genes in any organism is of considerable interest to the identification of the minimal assortment of genes required to sustain life and the identification of potential targets for new antimicrobial compounds. In a previous study, a total of 271 genes were deemed essential for growth of Bacillus subtilis in rich medium at 37°C (1). The criteria for classifying about 150 of these genes as essential were based on (i) the inability to interrupt the coding sequence by Campbell recombination of a plasmid bearing homology to a short (200-to 400-bp) internal portion of the gene and (ii) the strain becoming IPTG (isopropyl-␤-D-thiogalactopyranoside) dependent for growth when a Pspac promoter fusion was made to the intact gene by Campbell insertion of a similar plasmid bearing homology to the N-terminal portion of the coding sequence. Strains containing Pspac-dependent fusions to essential genes generally show significantly reduced growth in the absence of IPTG and essentially no growth if a plasmid expressing additional copies of the LacI repressor (e.g., pMAP65) is added to the strain. Residual growth, if observed, is usually attributed to leakiness of the Pspac promoter.In a follow-up study of 11 of these 150 putative essential genes, four genes of unknown function (ydiB, yloQ, yqeI, and ywlC) were deemed nonessential because they were successfully inactivated in a second attempt (2). However, at least three attempts to recover Campbell insertions for the 7 remaining genes (yacA, ydiC, ykqC, ylaN, ymdA, yneS, and yqjK) failed, while IPTG-dependent strains were successfully made. The essential nature of these genes was thus considered to be confirmed. Three of these genes, yqjK, ykqC, and ymdA, have since been shown to encode the ribonucleases...

The ubiquitous tripeptide Gly-Gly-Gln in class 1 polypeptide release factors triggers polypeptide release on ribosomes. The Gln residue in both bacterial and yeast release factors is N5-methylated, despite their distinct evolutionary origin. Methylation of eRF1 in yeast is performed by the heterodimeric methyltransferase (MTase) Mtq2p/Trm112p, and requires eRF3 and GTP. Homologues of yeast Mtq2p and Trm112p are found in man, annotated as an N6-DNA-methyltransferase and of unknown function. Here we show that the human proteins methylate human and yeast eRF1.eRF3.GTP in vitro, and that the MTase catalytic subunit can complement the growth defect of yeast strains deleted for mtq2. Structured summary:MINT-6571489: HemK2a (uniprotkb:Q9Y5N5) binds (MI:0407) to hTrm112 (uniprotkb:Q9UI30) by pull down (MI:0096)

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 , a founding member of the NYN (Nedd4-BP1/YacP nuclease) subfamily of PIN domain proteins, and identify potential substrates 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 ribosome and cleaves between specific codons of this mRNA Critically, we also demonstrate translation-dependent Rae1 cleavage of this substrate in a purified translation assay Multiple lines of evidence converge to suggest that Rae1 is an A-site endoribonuclease. We present a docking model of Rae1 bound to the ribosomal A-site that is consistent with this hypothesis and show that Rae1 cleaves optimally immediately upstream of a lysine codon (AAA or AAG) .

Ribosomal RNAs are processed from primary transcripts containing 16S, 23S and 5S rRNAs in most bacteria. Maturation generally occurs in a two-step process, consisting of a first crude separation of the major species by RNase III during transcription, followed by precise trimming of 5′ and 3′ extensions on each species upon accurate completion of subunit assembly. The various endo- and exoribonucleases involved in the final processing reactions are strikingly different in Escherichia coli and Bacillus subtilis, the two best studied representatives of Gram-negative and Gram-positive bacteria, respectively. Here, we show that the one exception to this rule is the protein involved in the maturation of the 3′ end of 16S rRNA. Cells depleted for the essential B. subtilis YqfG protein, a homologue of E. coli YbeY, specifically accumulate 16S rRNA precursors bearing 3′ extensions. Remarkably, the essential nature of YqfG can be suppressed by deleting the ribosomal RNA degrading enzyme RNase R, i.e. a ΔyqfG Δrnr mutant is viable. Our data suggest that 70S ribosomes containing 30S subunits with 3′ extensions of 16S rRNA are functional to a degree, but become substrates for degradation by RNase R and are eliminated.

No abstract

The recent findings that the narrow-specificity endoribonuclease RNase III and the 5′ exonuclease RNase J1 are not essential in the Gram-positive model organism, Bacillus subtilis, facilitated a global analysis of internal 5′ ends that are generated or acted upon by these enzymes. An RNA-Seq protocol known as PARE (Parallel Analysis of RNA Ends) was used to capture 5′ monophosphorylated RNA ends in ribonuclease wild-type and mutant strains. Comparison of PARE peaks in strains with RNase III present or absent showed that, in addition to its well-known role in ribosomal (rRNA) processing, many coding sequences and intergenic regions appeared to be direct targets of RNase III. These target sites were, in most cases, not associated with a known antisense RNA. The PARE analysis also revealed an accumulation of 3′-proximal peaks that correlated with the absence of RNase J1, confirming the importance of RNase J1 in degrading RNA fragments that contain the transcription terminator structure. A significant result from the PARE analysis was the discovery of an endonuclease cleavage just 2 nts downstream of the 16S rRNA 3′ end. This latter observation begins to answer, at least for B. subtilis, a long-standing question on the exonucleolytic versus endonucleolytic nature of 16S rRNA maturation.