Rif2 protects Rap1-depleted telomeres from MRX-mediated degradation in <i>Saccharomyces cerevisiae</i>.

Abstract

Rap1 is the main protein that binds double-stranded telomeric DNA in <i>Saccharomyces cerevisiae</i>. Examination of the telomere functions of Rap1 is complicated by the fact that it also acts as a transcriptional regulator of hundreds of genes and is encoded by an essential gene. In this study, we disrupt Rap1 telomere association by expressing a mutant telomerase RNA subunit (tlc1-tm) that introduces mutant telomeric repeats. <i>tlc1-tm</i> cells grow similar to wild-type cells, although depletion of Rap1 at telomeres causes defects in telomere length regulation and telomere capping. Rif2 is a protein normally recruited to telomeres by Rap1, but we show that Rif2 can still associate with Rap1-depleted <i>tlc1-tm</i> telomeres, and that this association is required to inhibit telomere degradation by the MRX complex. Rif2 and the Ku complex work in parallel to prevent <i>tlc1-tm</i> telomere degradation; <i>tlc1-tm</i> cells lacking Rif2 and the Ku complex are inviable. The partially redundant mechanisms may explain the rapid evolution of telomere components in budding yeast species.