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Exonuclease activity is required for sequence addition and Cdc13p loading at a de novo telomere

S J Diede1, D E Gottschling

  • 1Department of Pathology, The University of Chicago, Chicago, IL 60637, USA.

Current Biology : CB
|September 13, 2001
PubMed

Insights

The Saccharomyces cerevisiae Mre11p/Rad50p/Xrs2p (MRX) complex is crucial for telomere maintenance. MRX prepares telomeric DNA for Cdc13p binding, enabling telomere synthesis and protection.

Area of Science:

  • Molecular Biology
  • Genetics
  • Cell Biology

Background:

  • The conserved Saccharomyces cerevisiae Mre11p/Rad50p/Xrs2p (MRX) complex plays vital roles in DNA repair and telomere maintenance.
  • MRX complex is known to mediate DNA recombination at double-strand breaks (DSBs) via its 5' to 3' exonuclease activity.
  • Paradoxically, loss of this exonuclease activity in MRX mutants leads to telomere shortening, suggesting a complex role at telomeres.

Purpose of the Study:

  • To investigate the specific role of the MRX complex in telomere maintenance using a de novo telomere addition assay.
  • To elucidate the mechanism by which MRX influences telomere synthesis and protection.

Main Methods:

  • Analysis of MRX mutants in a de novo telomere addition assay in yeast cells.
  • Assessment of telomerase-mediated DNA addition in the presence and absence of functional MRX complex.
  • Evaluation of Cdc13p binding to de novo telomeric DNA substrates in MRX mutant cells.

Main Results:

  • The MRX complex genes were found to be essential for telomerase-mediated de novo telomere addition.
  • In cells lacking Rad50p (a component of the MRX complex), the single-stranded telomeric DNA binding protein Cdc13p could not bind to the telomeric substrate.
  • These findings indicate that MRX is required for the proper preparation of telomeric DNA.

Conclusions:

  • The MRX complex is indispensable for telomere elongation by telomerase.
  • MRX facilitates the binding of Cdc13p to telomeric DNA, which is critical for subsequent telomere synthesis and protection.
  • The MRX complex acts upstream of Cdc13p, preparing telomeric DNA for Cdc13p loading, chromosome protection, and telomerase recruitment.

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