The Arabidopsis core exosome (Exo9) has a phosphorolytic activity due to the RRP41 subunit. The goal of this experiment was to determine the role of this intrinsic activity of Exo9 on the maturation of the 5.8S rRNA in Arabidopsis. Overall design: We complemented the rrp41 null mutant by expressing either a wild type RRP41 transgene (RRP41WT) or transgenes encoding catalytic inactive versions (RRP41Pi- and RRP41Pi-Cat-). High density mapping of 5.8S rRNA precursors and mature 5.8S rRNA was performed using 3' RACE-seq. 3' RACE-seq is an IIlumina-based sequencing strategy designed to map 3' extremities (Sikorska et al. 2017). Mapping of 5.8S rRNA precursors was performed in rrp41 complemented lines and in several exosome mutants.