The artificial snoRNA construct, inserted in the intron of the actin gene and under the control of a GAL1 promoter, in the plasmid pRS416, was reported previously (24). C΄/D΄ regions, and the target site guide, were subsequently assembled from oligonucleotides and cloned into the NheI and MluI sites in the snoRNA coding sequence (Supplementary Figure S1). All experiments using these constructs were performed in S. cerevisiae strain W303 (leu2-3112 trp1-1 can1-100 ura3-1 ade2-1 his3-11,15).