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Gene Review

EST3  -  telomerase subunit EST3

Saccharomyces cerevisiae S288c

Synonyms: Ever shorter telomeres protein 3, Telomere replication protein EST3, YIL009C-A
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High impact information on EST3

  • Yeast telomerase is thought to be a holoenzyme containing Est2p and TLC1 RNA, the catalytic subunit and its intrinsic template, respectively, as well as the TLC1-RNA-associated factors Est1p and Est3p [1].
  • N-terminal domain of yeast telomerase reverse transcriptase: recruitment of Est3p to the telomerase complex [2].
  • Overexpression of telomerase component Est3p led to allele-specific suppression of the temperature-sensitive mutations in region I, suggesting that Est3p interacts with this protein domain [2].
  • In contrast, mutations in EST1, EST3 or CDC13 eliminate telomere replication in vivo [1] [6] [7] [8] but are dispensable for in vitro telomerase catalytic activity [2] [9] [3].
  • We show here that Est3p is a stable component of the telomerase holoenzyme and furthermore, association of Est3p with the enzyme requires an intact catalytic core [3].

Biological context of EST3

  • These data suggested that dimerization is important for Est3p function in vivo [4].
  • Double point mutation of Est3p-D49A-K68A and single point mutation of Est3p-K68A showed similar telomere shortening, suggesting that the K68 residue might be more important for telomerase activity [4].
  • The ectopic co-expression of K71A or T115A mutant with wild-type Est3p using centromere plasmids caused telomere shortening, while co-expression of the D49A, K68A, D86A or F103A mutants with wild-type Est3p had no effect on telomere length regulation [4].
  • RESULTS: We identified a potential site of +1 ribosomal frameshifting in the EST3 coding sequence and demonstrated that translation both upstream and downstream of this site is required for EST3 function [5].
  • Immunoblot analysis revealed that two proteins were synthesized from EST3: a truncated protein resulting from translation of only the first open reading frame, as well as the full-length 181 amino-acid Est3 protein resulting from translation through the frameshift site [5].

Anatomical context of EST3

  • These data suggest that the EST3 stimulator may modulate access by aminoacyl-tRNAs to the ribosomal A site by interacting with several targets in a ribosome paused during elongation [6].

Physical interactions of EST3

  • The absence of Est1p and Est3p from the complex during G1 phase can be attributed to proteasome-dependent degradation of Est1p [7].

Other interactions of EST3

  • EST1, EST2, EST3 and TLC1 function in a single pathway for telomere replication in the yeast Saccharomyces cerevisiae [1] [2], as would be expected if these genes all encode components of the same complex [3].
  • We find that frameshifting has persisted in two structural genes in budding yeasts, ABP140 and EST3 for about 150 million years [8].


  1. Telomerase: what are the Est proteins doing? Taggart, A.K., Zakian, V.A. Curr. Opin. Cell Biol. (2003) [Pubmed]
  2. N-terminal domain of yeast telomerase reverse transcriptase: recruitment of Est3p to the telomerase complex. Friedman, K.L., Heit, J.J., Long, D.M., Cech, T.R. Mol. Biol. Cell (2003) [Pubmed]
  3. The Est3 protein is a subunit of yeast telomerase. Hughes, T.R., Evans, S.K., Weilbaecher, R.G., Lundblad, V. Curr. Biol. (2000) [Pubmed]
  4. Saccharomyces cerevisiae Est3p dimerizes in vitro and dimerization contributes to efficient telomere replication in vivo. Yang, C.P., Chen, Y.B., Meng, F.L., Zhou, J.Q. Nucleic Acids Res. (2006) [Pubmed]
  5. Programmed translational frameshifting in a gene required for yeast telomere replication. Morris, D.K., Lundblad, V. Curr. Biol. (1997) [Pubmed]
  6. An mRNA sequence derived from the yeast EST3 gene stimulates programmed +1 translational frameshifting. Taliaferro, D., Farabaugh, P.J. RNA (2007) [Pubmed]
  7. Proteasome-dependent degradation of Est1p regulates the cell cycle-restricted assembly of telomerase in Saccharomyces cerevisiae. Osterhage, J.L., Talley, J.M., Friedman, K.L. Nat. Struct. Mol. Biol. (2006) [Pubmed]
  8. Evolution of +1 Programmed Frameshifting Signals and Frameshift-Regulating tRNAs in the Order Saccharomycetales. Farabaugh, P.J., Kramer, E., Vallabhaneni, H., Raman, A. J. Mol. Evol. (2006) [Pubmed]
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