%0 Journal Article %A Olombrada, Miriam %A Peña, Cohue %A Rodríguez-Galán, Olga %A Klingauf-Nerurkar, Purnima %A Portugal-Calisto, Daniela %A Oborská-Oplová, Michaela %A Altvater, Martin %A Gavilanes, José G %A Martínez-Del-Pozo, Álvaro %A de la Cruz, Jesús %A García-Ortega, Lucía %A Panse, Vikram Govind %T The ribotoxin α-sarcin can cleave the sarcin/ricin loop on late 60S pre-ribosomes. %D 2020 %U http://hdl.handle.net/10668/15496 %X 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. %~