Box H/ACA snoRNP complexes convert uridine to pseudouridine at 97 sites in human 28S, 18S, and 5.8S rRNAs (Kiss et al. 2004, reviewed in Ge and Yu 2013). The box H/ACA snoRNA component guides the complex to specific residues of the rRNAs by base pairing between the regions of the snoRNA and the rRNA (Kiss et al. 2004, Xiao et al. 2009). The human genome encodes more than 80 box H/ACA snoRNAs (Lestrade and Weber 2006).