Figure 1.

(A) Double-strand break repair defect in pku70⁻ and lig4⁻ strains. For each strain, the efficiency of repair is expressed as the number of transformants obtained with linear plasmid divided by the number of transformants obtained with circular plasmid. Numbers of colonies for a typical experiment were as follows: 1012 wild-type circular; 127 wild-type linear; 1160 pku70⁻ circular; 12 pku70⁻ linear; 1560 lig4⁻ circular; and 22 lig4⁻ linear. (B) Senescence and generation of survivors in the absence of telomerase and pku70⁺. A diploid strain heterozygous for deletions of pku70⁺ and trt1⁺ was sporulated, and the tetrads were dissected and germinated on YES plates. The resulting colonies were used to inoculate precultures in YES liquid medium. Growth curves were recorded as described in MATERIALS AND METHODS. Day 1 on the x axis corresponds to ∼30 generations after germination. The cell density on each day is plotted for wild type (▴), pku70⁻ trt1⁺ (▪ and □), pku70⁺ trt1⁻ (♦), and pku70⁻ trt1⁻ (● and ○). (C) As in B except that the diploid starter strain was heterozygous for deletions of lig4⁺ and trt1⁺. The cell density on each day is plotted for wild type (▴), lig4⁻ trt1⁺ (▪ and □), lig4⁺ trt1⁻ (♦), and lig4⁻ trt1⁻ (● and ○).