Template boundary definition in mammalian telomerase

Telomerase uses a short template sequence in its intrinsic RNA component to synthesize telomere repeats. Disruption of the helix Plb in human telomerase RNA or alteration of its distance from the template resulted in telomerase copying residues past the normal template boundary both in vivo and in vitro. Therefore, helix Plb is important for template boundary definition in human telomerase. Mouse telomerase RNA lacks helix Plb, and the boundary is established at 2 nt downstream of the 5′-end. The divergent structure of boundary definition elements in mammals, yeast, and ciliates suggests diverse mechanisms for template boundary definition in telomerase.