Reduction in rDNA copy number did not account for the suppression of <i>cdc6-4</i> by <i>sir2Δ</i>.

<p><b>A.</b> Diagram of a single rDNA repeat is shown with the location of the primer pairs used to assess rDNA copy number by qPCR indicated by colored histogram. The rDNA origin is indicated as the open circle. NTS are the non-transcribed regions in the rDNA locus. RFB is the replication fork block element that binds Fob1. <b>B.</b> Enrichment values are equal to 2^{- ΔCt} where ΔCt = Ct (rDNA locus (purple or teal) or <i>ERV46(</i>aqua<i>)</i>)—Ct (single copy control locus, <i>RIM15</i>) [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007418#pgen.1007418.ref072" target="_blank">72</a>] and equal the predicted average copy number of the target locus. For each strain, three independent colonies were assessed (biological replicates), each represented by a bar with the standard error. Because we observed substantial variation in rDNA copy number between colonies from the same strains (purple and teal bars represent different primer pairs that amplify the rDNA locus), we also used qPCR to assess the copy number of a single copy gene (<i>ERV46</i>) for the same DNA preparations (aqua). Note the different scale for the single-copy experiment as this value should equal only 1.0. <b>C.</b> <i>SIR2</i> effect on the average enrichment values of the rDNA locus for each of the strains assessed in C. <b>D.</b> Growth of 10-fold dilutions of the indicated strains was assessed on solid YPD media at the indicated temperatures. <b>E.</b> <i>SIR3</i> effect on the average enrichment values of the rDNA locus for each of the indicated strains.