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Bump-finder: identification of causal codons to the stalling of ribosomes

ABSTRACT: Stalling of the ribosomes on the mRNA has been linked to myriad of molecular and biological functions. While a multitude of algorithms predict codon-usage in ribosome profiling data, no tool exists to predict the context-specific stalling of ribosomes on transcripts. Combining these two features can reveal unprecedented insights in the ribosomal function and their usage across cells and conditions. To overcome this lack of tools to comprehensively analyze these features, we created Bumpfinder, a web-server, that provides comprehensive analytical details on differences in total ribosome occupancy on transcripts, ribosomal occupancy across codons, ribosome-stalling and the underlying causal amino-acids/codons, as well as collisions. Employing Bumpfinder on generated and publicly available ribosome-profiling datasets, we studied the response of various cell types to amino-acid starvation conditions. We observed interesting patterns in response to the biological effects, suggesting the impact of quality control mechanisms of protein synthesis. Complimentary analysis of collided ribosomes demonstrated phased ribosome stalling on the identified sites. Thus, by deciphering context-specific ribosome distribution, Bumpfinder provides unprecedented molecular insights in the ribosome function and mRNA translation during stress response conditions.

ORGANISM(S): Homo sapiens

PROVIDER: GSE156443 | GEO | 2023/12/31

REPOSITORIES: GEO

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Project description:Translation elongation rates are regulated to ensure proper conformation and biological function of proteins. Translation of either non-stop mRNA or transcripts coding for poly-basic sequences induces ribosome stalling, and the arrest product is degraded by the ribosome-mediated quality control system (RQC). During this process, the stalled ribosome is dissociated into subunits, and the polypeptide is ubiquitinated by the E3 ubiquitin ligase Listerin on the 60S large ribosomal subunit (LSU) leading to subsequent proteasomal degradation. However, it is largely unknown how stalled ribosomes are recognized and dissociated into subunits. Here we report that ubiquitination of the ribosomal protein uS10 by the E3 ubiquitin ligase Hel2 is required for the production of the RQC substrate. RQC-trigger (RQT) factors, a RNA helicase-family protein Slh1/Rqt2, ubiquitin binding protein Cue3/Rqt3 and yKR023W/Rqt4, were also required for the primary steps of RQC, and associated with Hel2-ribosome complexes. Rqt2-4 factors were dispensable for the ubiquitination of uS10 by Hel2/Rqt1 and associated with ribosomes independent of the ubiquitination of uS10. However, the ubiquitin-binding activity of Rqt3 were crucial to trigger RQC. Cryo-electron microscopy (cryo-EM) analysis revealed that Hel2 bound ribosomes are in an rotated state containing hybrid state AP- and PE-tRNAs. Furthermore, ribosome profiling revealed that short footprints, hallmarks of hybrid state ribosomes18, were accumulated at tandem CGA rare codons at the beginning of the poly arginine stalling sequence and long footprints at subsequent codons, respectively. Short footprints at CGA codons were decreased in rqt1 mutant but drastically increased in uS10 mutants defective in the ubiquitination or rqt2 mutant. Collectively, our results demonstrate that Hel2 stabilizes ratcheted ribosomes leading to ubiquitination of uS10. Subsequently, Rqt2-4 factors target these hybrid state ribosomes specifically, allowing subsequent RQC reactions.

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Bump-finder: identification of causal codons to the stalling of ribosomes

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