Fig. 3. Rif2 negatively regulates replicative senescence through the MRX pathway.

(A) Relative senescence scores for tlc1-Δ rif2-Δ (22 isolates) compared to tlc1-Δ (18 isolates). (B) Relative senescence scores for the indicated strains, derived from an average of two experiments (with a minimum of 25 isolates per genotype for each experiment); Fig. S2 shows statistical data for the comparison between rad50-Δ and rad50-Δ rif2-Δ for each of the two experiments. The apparent lack of an effect at the 25 generation time point for tlc1-Δ rad50-Δ (and similarly for tlc1-Δ tel1-Δ, in part C), indicated by asterisks, was a consequence of slightly elongated telomeres in the parental diploid strains (due to rif2-Δ/RIF2 haploinsufficiency; data not shown), which delayed the appearance of the senescence phenotype in the resulting tlc1-Δ and tlc1-Δ rad50-Δ isolates. (C) Relative senescence scores of the indicated strains generated following dissection of a tlc1-Δ/TLC1 rif2-Δ/RIF2 tel1-Δ/TEL1 diploid strain; an independent repeat of this experiment is shown in Fig. S2. (D) Genetic map of the epistatic relationship between Tel1, Rif2 and MRX; the severity of the replicative senescence phenotype in response to mutations in factors in the pathway is schematically represented by the size of the box.