Figure 5.

(A) Comparison of template boundary definition elements among human, mouse, yeast, and ciliate telomerase RNAs. The known secondary structures of regions flanking the RNA template are depicted for human, mouse, Kluyveromyces lactis (yeast), and Tetrahymena thermophila (ciliate) telomerase RNAs. The sequence of the template region is shown in a black box, and the RNA structure essential for template boundary definition is shown in a red box with a red line to indicate function in boundary definition. (B) A proposed model for template boundary definition in human telomerase. The TERT protein is depicted as a gray sphere with the catalytic site shown as an open circle. The helix P1b (shown in blue) serves as an anchor point for tethering the linker (shown in blue) and the template region (white box). During the copying of the template, the movement of the RNA template within the catalytic site is constrained by the length of the linker region.