Telomeric protein distributions and remodeling through the cell cycle in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, telomeric DNA is protected by a nonnucleosomal protein complex, tethered by the protein Rap1. Rif and Sir proteins, which interact with Rap1p, are thought to have further interactions with conventional nucleosomic chromatin to create a repressive structure that protects the chromosome end. We showed by microarray analysis that Rif1p association with the chromosome ends extends to subtelomeric regions many kilobases internal to the terminal telomeric repeats and correlates strongly with the previously determined genomic footprints of Rap1p and the Sir2-4 proteins in these regions. Although the end-protection function of telomeres is essential for genomic stability, telomeric DNA must also be copied by the conventional DNA replication machinery and replenished by telomerase, suggesting that transient remodeling of the telomeric chromatin might result in distinct protein complexes at different stages of the cell cycle. Using chromatin immunoprecipitation, we monitored the association of Rap1p, Rif1p, Rif2p, and the protein component of telomerase, Est2p, with telomeric DNA through the cell cycle. We provide evidence for dynamic remodeling of these components at telomeres.