(A) Structure of human telomerase H/ACA RNP. Proteins are shown in surface representation and hTR is shown in cartoon representation. (B) Dyskeratosis congenita (DC) disease mutations mapped onto the human telomerase H/ACA RNP structure. Residues whose mutations are associated with DC disease are shown as spheres and coloured according to the associated subunits as indicated. (C,D) Cartoon schematics of telomerase H/ACA RNP and a proposed canonical H/ACA RNP, respectively. (E,F) Structures of the 5′ and 3′ H/ACA RNA hairpins of telomerase bound to their corresponding H/ACA heterotetramers, respectively. The cartoon schematics are also shown on the right corner of each panel. This illustrates the reduced protein–RNA interactions at the 5′ hairpin of telomerase H/ACA RNA.