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  • Title: The ribotoxin α-sarcin can cleave the sarcin/ricin loop on late 60S pre-ribosomes.
    Author: Olombrada M, Peña C, Rodríguez-Galán O, Klingauf-Nerurkar P, Portugal-Calisto D, Oborská-Oplová M, Altvater M, Gavilanes JG, Martínez-Del-Pozo Á, de la Cruz J, García-Ortega L, Panse VG.
    Journal: Nucleic Acids Res; 2020 Jun 19; 48(11):6210-6222. PubMed ID: 32365182.
    Abstract:
    The ribotoxin α-sarcin belongs to a family of ribonucleases that cleave the sarcin/ricin loop (SRL), a critical functional rRNA element within the large ribosomal subunit (60S), thereby abolishing translation. Whether α-sarcin targets the SRL only in mature 60S subunits remains unresolved. Here, we show that, in yeast, α-sarcin can cleave SRLs within late 60S pre-ribosomes containing mature 25S rRNA but not nucleolar/nuclear 60S pre-ribosomes containing 27S pre-rRNA in vivo. Conditional expression of α-sarcin is lethal, but does not impede early pre-rRNA processing, nuclear export and the cytoplasmic maturation of 60S pre-ribosomes. Thus, SRL-cleaved containing late 60S pre-ribosomes seem to escape cytoplasmic proofreading steps. Polysome analyses revealed that SRL-cleaved 60S ribosomal subunits form 80S initiation complexes, but fail to progress to the step of translation elongation. We suggest that the functional integrity of a α-sarcin cleaved SRL might be assessed only during translation.
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