FIGURE 1.

Box H/ACA RNP bound (base-paired) with its substrate RNA. Box H/ACA RNA (thin line) folds into a hairpin-hinge (containing an H box)-hairpin-tail (containing an ACA box) structure. The substrate RNA (thick line) is also shown. The internal loop (pseudouridylation pocket) of each hairpin base pairs with the substrate RNA, positioning the target U (arrow) and its immediate 3′ nucleotide (N) at the base of the upper stem (the dinucleotide is left unpaired). The four core box H/ACA RNP proteins, Nhp2, Nop10, Gar1, and Cbf5 (pseudouridylase), are also shown. Further illustrated is the internal loop (pseudouridylation pocket) within the 5′ hairpin, where the 5′ side and 3′ side of the pseudouridylation pocket as well as the base pairs immediately 5′ and 3′ of the unpaired dinucleotide UN (substrate) are indicated.