Figure 2.—

The sir2-276 mutation has a temperature-sensitive silencing defect at the HM loci. Expression from the HM loci of SIR2, sir2Δ, or sir2-276 strains was determined by RT–PCR. (A) cDNA derived from RNA from MATα strains (W303-1b, RS1717, and RS2291) grown at either 25° or 37° was amplified with primers to a1 and PMA1. The a1/PMA1 ratios were calculated and shown relative to the value for the sir2Δ strain, which was set to 1. (B) cDNA from MATa strains (W303-1a, RS869, and RS2292) cultured at either 25° or 37° was amplified with primers to α1 and PMA1. The α1/PMA1 ratios were calculated and shown as in A.