Rap1p telomere association is not required for mitotic stability of a C₃TA₂ telomere in yeast

Telomeric DNA usually consists of a repetitive sequence: C_1-3A/TG_1-3 in yeast, and C₃TA₂/T₂AG₃ in vertebrates. In yeast, the sequence-specific DNA-binding protein Rap1p is thought to be essential for telomere function. In a tlc1h mutant, the templating region of the telomerase RNA gene is altered so that telomerase adds the vertebrate telomere sequence instead of the yeast sequence to the chromosome end. A tlc1h strain has short but stable telomeres and no growth defect. We show here that Rap1p and the Rap1p-associated Rif2p did not bind to a telomere that contains purely vertebrate repeats, while the TG_1-3 single-stranded DNA binding protein Cdc13p and the normally non-telomeric protein Tbf1p did bind this telomere. A chromosome with one entirely vertebrate-sequence telomere had a wild-type loss rate, and the telomere was maintained at a short but stable length. However, this telomere was unable to silence a telomere-adjacent URA3 gene, and the strain carrying this telomere had a severe defect in meiosis. We conclude that Rap1p localization to a C₃TA₂ telomere is not required for its essential mitotic functions.