Flow cytometry validation of opposing effects of lengthening poly(dA:dT) tracts and strengthening transcription factor binding sites. (A) Strengthening the affinity of a transcription factor binding site mainly affects burst size. For two different sets of promoter variants, each with three different binding site affinities for Gcn4, shown are the values of the two parameters from the Gamma function when fitted to the normalized YFP intensities of each promoter variant measured over the cell population at a single time point using a flow cytometer. Under certain assumptions (Friedman et al. 2006; Taniguchi et al. 2010), these two parameters correspond to the burst frequency (left graph) and burst size (right graph). Note the larger variation in burst size across these variants. (B) Same as A, for variants in which the affinities of Gal4 binding sites were varied. (C) Lengthening a poly(dA:dT) tract mainly affects burst frequency. Same as A, for variants in which the length of a poly(dA:dT) tract was varied. In contrast to A and B, note the larger variation in burst frequency across these variants. [R0, right poly(dA:dT) deleted; L0, left poly(dA:dT) deleted.]
