FIGURE 1: Structure of the yeast telomere.

(A) Schematic representation of a yeast telomere. All yeast chromosomes carry subtelomeric repeats called X elements, and between 0 and 4 copies of another sub-telomeric element, the Y’ sequences. Telomeric repeats are composed of variations of the T(G1-3) formula. The TG-rich strand (with its 3’ OH) is longer than the complementary strand (TG overhangs).

(B) Schematic representation of the telomeric chromatin, with representative proteins. Rap1 binds the telomeric repeats, and Rif1, Rif2 and the SIR proteins bind to Rap1. The Ku heterodimer binds to telomeric dsDNA and the CST complex binds the terminal ssDNA end. Telomerase is recruited to telomeres present in an “extensible” configuration by interactions with the CST.