No abstract

In eukaryotes, termination of messenger RNA (mRNA) translation is mediated by the release factors eRF1 and eRF3. Using Saccharomyces cerevisiae as a model organism, we have identified a member of the DEAD-box protein (DBP) family, the DEAD-box RNA helicase and mRNA export factor Dbp5, as a player in translation termination. Dbp5 interacts genetically with both release factors and the polyadenlyate-binding protein Pab1. A physical interaction was specifically detected with eRF1. Moreover, we show that the helicase activity of Dbp5 is required for efficient stop-codon recognition, and intact Dbp5 is essential for recruitment of eRF3 into termination complexes. Therefore, Dbp5 controls the eRF3-eRF1 interaction and thus eRF3-mediated downstream events.

The iron-sulphur (Fe-S)-containing RNase L inhibitor (Rli1) is involved in ribosomal subunit maturation, transport of both ribosomal subunits to the cytoplasm, and translation initiation through interaction with the eukaryotic initiation factor 3 (eIF3) complex. Here, we present a new function for Rli1 in translation termination. Through co-immunoprecipitation experiments, we show that Rli1 interacts physically with the translation termination factors eukaryotic release factor 1 (eRF1)/Sup45 and eRF3/Sup35 in Saccharomyces cerevisiae. Genetic interactions were uncovered between a strain depleted for Rli1 and sup35-21 or sup45-2. Furthermore, we show that downregulation of RLI1 expression leads to defects in the recognition of a stop codon, as seen in mutants of other termination factors. By contrast, RLI1 overexpression partly suppresses the read-through defects in sup45-2. Interestingly, we find that although the Fe-S cluster is not required for the interaction of Rli1 with eRF1 or its other interacting partner, Hcr1, from the initiation complex eIF3, it is required for its activity in translation termination; an Fe-S cluster mutant of RLI1 cannot suppress the read-through defects of sup45-2.

No abstract

In Saccharomyces cerevisiae, deletion of large ribosomal subunit protein-encoding genes increases the replicative lifespan in a Gcn4-dependent manner. However, how Gcn4, a key transcriptional activator of amino acid biosynthesis genes, increases lifespan, is unknown. Here we show that Gcn4 acts as a repressor of protein synthesis. By analyzing the messenger RNA and protein abundance, ribosome occupancy and protein synthesis rate in various yeast strains, we demonstrate that Gcn4 is sufficient to reduce protein synthesis and increase yeast lifespan. Chromatin immunoprecipitation reveals Gcn4 binding not only at genes that are activated, but also at genes, some encoding ribosomal proteins, that are repressed upon Gcn4 overexpression. The promoters of repressed genes contain Rap1 binding motifs. Our data suggest that Gcn4 is a central regulator of protein synthesis under multiple perturbations, including ribosomal protein gene deletions, calorie restriction, and rapamycin treatment, and provide an explanation for its role in longevity and stress response.

No abstract

Regulation of cell growth is a fundamental process in development and disease that integrates a vast array of extra- and intracellular information. A central player in this process is RNA polymerase I (Pol I), which transcribes ribosomal RNA (rRNA) genes in the nucleolus. Rapidly growing cancer cells are characterized by increased Pol I–mediated transcription and, consequently, nucleolar hypertrophy. To map the genetic network underlying the regulation of nucleolar size and of Pol I–mediated transcription, we performed comparative, genome-wide loss-of-function analyses of nucleolar size in Saccharomyces cerevisiae and Drosophila melanogaster coupled with mass spectrometry–based analyses of the ribosomal DNA (rDNA) promoter. With this approach, we identified a set of conserved and nonconserved molecular complexes that control nucleolar size. Furthermore, we characterized a direct role of the histone information regulator (HIR) complex in repressing rRNA transcription in yeast. Our study provides a full-genome, cross-species analysis of a nuclear subcompartment and shows that this approach can identify conserved molecular modules.

Introduction Predominantly uncontrolled studies suggest that there may be a greater risk of subsequent vertebral compression fractures (VCFs) associated with vertebroplasty and kyphoplasty. To further understand the risk of VCFs, we conducted a population-based retrospective cohort study using data from a large regional health insurer. Materials and Methods Administrative claims procedure codes were used to identify a treatment group of patients receiving either a vertebroplasty or kyphoplasty (treatment group) and a comparison group of patients with a primary diagnosis of VCF who did not receive treatment during the same time period. The main outcomes of interest, validated by two independent medical record reviewers and adjudicated by a physician panel, were any new VCFs within: 1) 90-days; 2) 360-days; and 3) at adjacent vertebral levels. Multivariable logistic regression examined the association of vertebroplasty/kyphoplasty with new VCFs. Results Among 48 treatment (51% vertebroplasty, 49% kyphoplasty) and 164 comparison patients, treated patients had a significantly greater risk of secondary VCFs than comparison patients for fractures within 90 days of the procedure or comparison group time point (adjusted odds ratio (OR) = 6.3; 95% confidence interval (CI) 1.7 – 23.0) and within 360 days (adjusted OR = 3.1; 95% CI:1.1 – 8.4). Vertebroplasty and kyphoplasty were associated with a significantly greater rate of adjacent-level fractures as well. Conclusions Patients who had undergone vertebroplasty and kyphoplasty had a greater risk of new VCFs compared to patients with prior VCFs who did not undergo either procedure.