Figure 7. DNA end binding–defective mutants are deficient for telomeric silencing.

(A) Telomeric silencing assay in DNA end binding defective strains. Shown are five-fold serial dilutions of an EXO1 yku70-Δ yku80-Δ strain with VII-L URA3 and V-R ADE2 telomeric reporters (YAB219) transformed with plasmids containing vector, WT, or mutant versions of YKU70 (TRP1) and YKU80 (LEU2). Growth was monitored on –Trp –Leu –Ura at 28°C to examine de-repression of URA3 (-uracil plates) and on –Trp –Leu at 28°C to monitor plating efficiency (+uracil plates) and 37°C as a surrogate marker for telomere end protection (37°C plates) [26]. Growth was also examined on –Trp –Leu media with limiting Ade to examine de-repression of ADE2 (low ade plates). (B) Telomeric silencing assay in DNA end binding defective strains lacking EXO1. Experiment was performed as described in A, except the plasmids were transformed into an exo1-Δ yku70-Δ yku80-Δ telomeric reporter strain (YAB353).