FIG. 7.
SNF2 is required for telomeric silencing. (A) Telomeric silencing phenotypes determined using a telomeric URA3 reporter gene. Tenfold serial dilutions of stationary-phase cultures of wild-type (L1087 and L1088), sir2Δ (L1091 and L1092), or snf2Δ (L1089 and L1090) strains containing the URA3 at the right telomere of chromosome V were spotted onto 5-FOA and YPD medium to monitor expression of the URA3. Loss of silencing is indicated by reduced growth on 5-FOA. (B) Swi/Snf represses URA3 transcription at the telomere. Strains with URA3 at its normal genomic location (lane 1) or integrated at the right telomere of chromosome V (lanes 2 to 7) were grown in SC medium supplemented with 100 mg of uracil/liter. mRNA levels of URA3 and the loading control, ACT1, were measured by Northern analysis. The strains used in the experiment were as follows: lane 1, FY78; lane 2, L1091; lane 3, L1092; lane 4, L1087; lane 5, L1088; lane 6, L1089; and lane 7, L1090. The quantitation represents the relative level of URA3 mRNA normalized to the level of ACT1. The numbers represent the averages for the pairs of strains shown. wt, wild type. (C) Swi/Snf has no detectable effect on HMLα silencing. Three MATa strains in lanes 1 to 3 (wild type [wt], FY78; snf2Δ, FY328; snf5Δ, FY1658) and a MATα strain, FY1856, were grown in YPD to 2 × 107 cells/ml. α1 and ACT1 mRNA levels were measured by Northern analysis.