The telomere capping complex CST has an unusual stoichiometry, makes multipartite interaction with G-Tails, and unfolds higher-order G-tail structures

PLoS Genet. 2013;9(1):e1003145. doi: 10.1371/journal.pgen.1003145. Epub 2013 Jan 3.

Abstract

The telomere-ending binding protein complex CST (Cdc13-Stn1-Ten1) mediates critical functions in both telomere protection and replication. We devised a co-expression and affinity purification strategy for isolating large quantities of the complete Candida glabrata CST complex. The complex was found to exhibit a 2∶4∶2 or 2∶6∶2 stoichiometry as judged by the ratio of the subunits and the native size of the complex. Stn1, but not Ten1 alone, can directly and stably interact with Cdc13. In gel mobility shift assays, both Cdc13 and CST manifested high-affinity and sequence-specific binding to the cognate telomeric repeats. Single molecule FRET-based analysis indicates that Cdc13 and CST can bind and unfold higher order G-tail structures. The protein and the complex can also interact with non-telomeric DNA in the absence of high-affinity target sites. Comparison of the DNA-protein complexes formed by Cdc13 and CST suggests that the latter can occupy a longer DNA target site and that Stn1 and Ten1 may contact DNA directly in the full CST-DNA assembly. Both Stn1 and Ten1 can be cross-linked to photo-reactive telomeric DNA. Mutating residues on the putative DNA-binding surface of Candida albicans Stn1 OB fold domain caused a reduction in its crosslinking efficiency in vitro and engendered long and heterogeneous telomeres in vivo, indicating that the DNA-binding activity of Stn1 is required for telomere protection. Our data provide insights on the assembly and mechanisms of CST, and our robust reconstitution system will facilitate future biochemical analysis of this important complex.

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

  • Candida albicans / genetics
  • Candida albicans / metabolism
  • Candida glabrata / genetics*
  • Candida glabrata / metabolism
  • Cell Cycle Proteins* / genetics
  • Cell Cycle Proteins* / metabolism
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism
  • DNA Replication
  • Fungal Proteins / chemistry*
  • Fungal Proteins / genetics*
  • Protein Binding
  • Protein Folding
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins* / genetics
  • Saccharomyces cerevisiae Proteins* / metabolism
  • Telomere / genetics*
  • Telomere / metabolism
  • Telomere-Binding Proteins / chemistry*
  • Telomere-Binding Proteins / genetics*
  • Telomere-Binding Proteins / metabolism

Substances

  • Cdc13 protein, S cerevisiae
  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • Fungal Proteins
  • Saccharomyces cerevisiae Proteins
  • Stn1 protein, S cerevisiae
  • TEN1 protein, S cerevisiae
  • Telomere-Binding Proteins