Homo sapiens U100 scaRNA. This H/ACA box RNA was originally cloned from a mouse brain library by Huttenhofer et al. (2001) and named MBII-201. Its human ortholog, U100, was characterized by Northern blot and was localized by FISH to Cajal bodies. From base-pairing prediction, it could guide the pseudouridylation of the U6 residue in the U6 spliceosomal snRNA. However, it was verified that this base is not pseudouridylated (Vitalli et al., 2003). Schattner et al. (2006) predicted that U100 guides the pseudouridylation of U2 snRNA U7.