Telomerase elongation model. (1) Telomerase recognized the telomere substrate, and the terminal d(TTGGGG) repeat is base-paired with the CAACCCCAA RNA template. (2) The RNA is copied to the end of the template region. (3) Translocation repositions the terminal TTGGGGTTG sequence and exposes additional template sequences. (4) Another round of template copying produces addtional TTGGGG repeats.