Schematic depiction of the predicted secondary structure of hTERC. This schematic depiction is as proposed by Chen et al.²  The 8-base template sequence (rectangle) and other structural features are indicated, including the core, CR4-CR5, box H/ACA, and CR7 domains, and the hypervariable paired region. Mutations associated with DC are indicated in red; those associated with AA, MDS, or PNH are in green. The G228A and G58A variants (in blue) are fully active in vitro (Fu and Collins,¹⁷  Marrone et al,²⁷  and the present study) and also found in healthy individuals, and may be functionally inconsequential. Δ denotes nucleotide deletion (see Figure 2A for details). Nucleotide deletions are indicated by thick lines, whereas boxed regions show a large deletion that completely removes the sequences of the box H/ACA and CR7 domains.