Reporter gene expression driven by various combinations of Cbf1 and Met31/32 binding sites. (A) Yeast strains were grown under either repressive (+Met) or activating (-Met) growth conditions, in addition to varying concentrations of the inhibitor, 3-AT. Each column represents a 10-fold serial dilution of a yeast strain containing a reporter plasmid with a different binding site combination, labeled as follows. V: vector alone, C: Cbf1 binding site, M: Met31/32 binding site, C2: Two Cbf1 binding sites spaced by 35 bp, M2: Two Met31/32 binding sites spaced by 35 bp, CM: Cbf1 binding site placed 35 bp upstream of a Met31/32 binding site, MC: Met31/32 binding site placed 35 bp upstream of a Cbf1 binding site. Yeast strains were grown on the indicated media for 5 days at 30°C. Serial dilutions were performed in triplicate, and a representative dilution is displayed for each growth condition. (B) Average inferred transcript levels in sulfur-limitation conditions associated with various promoter architectures. For each gene, the gene expression log ratio between sulfur limitation and complete media conditions was calculated as the average log base 2 expression ratio from previously published gene expression studies [28, 29]. To infer the average number of mRNA transcripts per cell, the gene expression ratio for each gene was multiplied by the basal transcript level as measured during growth in rich media . Inferred transcript levels were averaged over sets of genes that shared the indicated binding site combinations in the 500 bp upstream of their translation start sites; the first row indicates the average for all genes. Error bars indicate the standard error of the mean.