TPP1 is a component of the telomerase holoenzyme, involved in telomere replication. It has been demonstrated that TPP1 dimerises and binds to DNA and RNA. Furthermore, TPP1 stimulates the dissociation of RNA/DNA hetero-duplexes [1,2]. Yeast telomerase protein TPP1 (Est3 in yeast) is a novel type of GTPase [3]. The key residues in Swiss:Q03096 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 [4]. 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 [5,6]. This domain is conserved from fungi to mammals, hence family Telomere_Pot1 has been merged into the family [7]. 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) [8].

1: Saccharomyces cerevisiae Est3p dimerizes in vitro and dimerization contributes to efficient telomere replication in vivo. Yang CP, Chen YB, Meng FL, Zhou JQ; Nucleic Acids Res. 2006;34:407-416. PMID:16418502

2: Saccharomyces cerevisiae telomerase subunit Est3p binds DNA and RNA and stimulates unwinding of RNA/DNA heteroduplexes. Sharanov YS, Zvereva MI, Dontsova OA; FEBS Lett. 2006;580:4683-4690. PMID:16884717

3: Yeast telomerase protein Est3 is a novel type of GTPase. Shubernetskaya O, Logvina N, Sharanov Y, Zvereva M; Biochimie. 2010; [Epub ahead of print] PMID:20884318

4: POT1-interacting protein PIP1: a telomere length regulator that recruits POT1 to the TIN2/TRF1 complex. Ye JZ, Hockemeyer D, Krutchinsky AN, Loayza D, Hooper SM, Chait BT, de Lange T; Genes Dev. 2004;18:1649-1654. PMID:15231715

5: The POT1-TPP1 telomere complex is a telomerase processivity factor. Wang F, Podell ER, Zaug AJ, Yang Y, Baciu P, Cech TR, Lei M; Nature. 2007;445:506-510. PMID:17237768

6: Functional interaction between telomere protein TPP1 and telomerase. Zaug AJ, Podell ER, Nandakumar J, Cech TR; Genes Dev. 2010;24:613-622. PMID:20231318

7: Fission yeast Pot1-Tpp1 protects telomeres and regulates telomere length. Miyoshi T, Kanoh J, Saito M, Ishikawa F; Science. 2008;320:1341-1344. PMID:18535244

8: The telomere syndromes. Armanios M, Blackburn EH; Nat Rev Genet. 2012;13:693-704. PMID:22965356