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Molecular interactions between Hel2 and RNA supporting ribosome-associated quality control [II]

ABSTRACT: Ribosome-associated quality control (RQC) pathways monitor and respond to stalling of translating ribosomes. Using a newly developed technique based on in vivo UV crosslinking and mass spectrometry, we identify a C-terminal region in Hel2/Rqt1 as an RNA binding domain, with amino acids L501/K502 directly interacting with RNA. In vivo crosslinking of Hel2 revealed binding to 18S rRNA and translating mRNAs. Consistent with the 18S binding site located between mRNA entrance and exit channels, Hel2 preferentially bound mRNA both upstream and downstream of the termination codon. A C-terminal truncation that deleted L501/K502, abolished crosslinking to 18S rRNA, altered mRNA binding patterns, and reduced Hel2 function comparable to hel2∆. Asc1, also participates in RQC and ASC1 deletion impaired Hel2 18S and mRNA binding. We conclude that Hel2 is recruited or stabilized on translating 40S ribosomal subunits by interactions with 18S rRNA and Asc1. Ribosome-bound Hel2 interacts with mRNA, predominately during translation termination.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE114420 | GEO | 2019/01/18

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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Molecular interactions between Hel2 and RNA supporting ribosome-associated quality control [II]

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