Figure 1.

A genetic screen identifies genes required for telomerase activity. (A) Demonstration of the feasibility of the rad52 synthetic lethal screen. tlc1Δ rad52Δ haploid yeast harboring a plasmid expressing Rad52 protein were aged for 40, 60, or 80 generations and replica-plated on medium lacking uracil (Ura⁻) to retain the RAD52 plasmid (Upper) or on FOA to evict the RAD52 plasmid (Lower). (B) Identification of mutant clones with short telomeres (∗). Telomere hybridization analysis of XhoI-digested genomic DNA isolated from a subset of mutant clones that depend upon the RAD52-expressing plasmid for viability. The bulk of the wild-type (wt) telomeres appear as heterogeneous size fragments at ≈1.3 kbp. (C) Identification of a mutant clone lacking telomerase activity. Extracts were isolated from wild-type (WT) parental strain Y0025, from a tlc1Δ strain, and from mutant clone 8 and were incubated with (lane 2) or without (lanes 1, 3, and 4) RNase prior to assaying telomerase activity. Position of the γ-³²P-labeled primer is shown on the left.