Tetrahymena telomerase holoenzyme assembly, activation, and inhibition by domains of the p50 central hub

Mol Cell Biol. 2013 Oct;33(19):3962-71. doi: 10.1128/MCB.00792-13. Epub 2013 Aug 5.


The eukaryotic reverse transcriptase, telomerase, adds tandem telomeric repeats to chromosome ends to promote genome stability. The fully assembled telomerase holoenzyme contains a ribonucleoprotein (RNP) catalytic core and additional proteins that modulate the ability of the RNP catalytic core to elongate telomeres. Electron microscopy (EM) structures of Tetrahymena telomerase holoenzyme revealed a central location of the relatively uncharacterized p50 subunit. Here we have investigated the biochemical and structural basis for p50 function. We have shown that the p50-bound RNP catalytic core has a relatively low rate of tandem repeat synthesis but high processivity of repeat addition, indicative of high stability of enzyme-product interaction. The rate of tandem repeat synthesis is enhanced by p50-dependent recruitment of the holoenzyme single-stranded DNA binding subunit, Teb1. An N-terminal p50 domain is sufficient to stimulate tandem repeat synthesis and bridge the RNP catalytic core, Teb1, and the p75 subunit of the holoenzyme subcomplex p75/p19/p45. In cells, the N-terminal p50 domain assembles a complete holoenzyme that is functional for telomere maintenance, albeit at shortened telomere lengths. Also, in EM structures of holoenzymes, only the N-terminal domain of p50 is visible. Our findings provide new insights about subunit and domain interactions and functions within the Tetrahymena telomerase holoenzyme.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Catalytic Domain
  • Electrophoresis, Polyacrylamide Gel
  • Holoenzymes / chemistry
  • Holoenzymes / metabolism*
  • Holoenzymes / ultrastructure
  • Imaging, Three-Dimensional
  • Microscopy, Electron
  • Models, Molecular
  • Protein Binding
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / metabolism*
  • Protozoan Proteins / ultrastructure
  • Ribonucleoproteins / chemistry
  • Ribonucleoproteins / metabolism
  • Ribonucleoproteins / ultrastructure
  • Tetrahymena / enzymology*


  • Holoenzymes
  • Protein Subunits
  • Protozoan Proteins
  • Ribonucleoproteins