TPP1 is a component of the telomerase holoenzyme, involved in telomere replication. It has been demonstrated that TPP1 dimerizes and binds to DNA and RNA. Furthermore, TPP1 stimulates the dissociation of RNA/DNA hetero-duplexes. Yeast telomerase protein TPP1 (Est3 in yeast) is a novel type of GTPase. The key residues in yeast EST3 are an Asp at residue 86 and the Arg at residue 110. The Asp is totally conserved in the family, whereas the Arg is not so well conserved. The N-terminal of TPP1 is likely to be the binding surface for TINF2, whereas the C-terminus probably binds to POT1, thereby tethering POT1 to the shelterin complex. The complex bound to telomeric DNA increases the activity and processivity of the human telomerase core enzyme, thus helping to maintain the length of the telomeres. This domain is conserved from fungi to mammals, hence family Telomere_Pot1 has been merged into the family. The human shelterin complex includes six proteins: telomere repeat binding factor 1 (TRF1), TRF2, repressor/activator protein 1 (RAP1), TRF1-interacting nuclear protein 2 (TIN2), TIN2-interacting protein 1 (TPP1) and protection of telomeres 1 (POT1).