FIG. 1.

Tor1 is required for gene silencing and maintenance of telomere length. (A) The set of genes upregulated by loss of Tor1 significantly overlaps with the set of genes upregulated in histone deacetylase mutants. The number of genes that were upregulated 1.5-fold in the indicated mutants is presented in Venn diagrams, along with corresponding P values. (B) Northern blot analysis. Total RNA was prepared from wild-type (WT), Δtor1, and clr6-1 mutants grown to mid-log phase in rich medium. Northern blots were probed with the indicated genes. (C) Tor1 promotes silencing at the mating type locus. Strains containing an ade6⁺ cassette at the mating type locus were spotted onto the indicated plates. In an otherwise wild-type background, the ade6⁺ gene insertion produced a typical position variegation effect, since only a portion of the colonies is white (express the ade6⁺ gene) while others are red due to a decreased level of ade6⁺ transcript and accumulation of a red pigment. Only white colonies are present in cells carrying the Δtor1 mutation. (D) Tor1 is required for tolerance to microtubule destabilizing agents. Cells were streaked on plates containing the indicated levels of TBZ. (E) Tor1 is required for the maintenance of telomere length regulation. DNA was extracted from cells grown in rich medium (or minimal medium; asterisk). When rapamycin was added (R), the cells were grown in the presence of 100 ng/ml rapamycin. Genomic DNA was digested with EcoRI, which in wild-type cuts about 1 kb from the terminus, and analyzed by Southern blotting. The resulting filter was probed with α³²-P-labeled telomere repeat DNA.