Bimodality of gene expression from yeast promoter can be instigated by DNA context, inducing conditions and strain...

Bimodality in gene expression is thought to provide a high phenotypic heterogeneity that can be favourable for adaptation or unfavourable notably in industrial processes that require stable and homogeneous properties. Whether this property is produced or suppressed in different conditions has been understudied. Here we identified tens of Saccharomyces cerevisiae genomic fragments conferring bimodal yEGFP expression on centromeric plasmid and studied some of these promoters in different DNA contexts, inducing conditions or strain backgrounds. First, we observed that the bimodal behaviour identified on plasmid is generally suppressed at the genomic level. Second, an inducible promoter such as the copper-regulated CUP1 promoter can produce bimodal expression in a time- and dose-dependent fashion. For a given copper sulphate concentration, a constant proportion of the subpopulation is induced and only the induction level of this subpopulation changed with induction duration, while for a same induction time, higher copper sulphate concentrations induced more cells at higher levels. Third, we showed that bimodality conferred by the CUP1 promoter in expression profile is strain background dependent, revealing epistasis in the generation of bimodality. The influence of these parameters on bimodality has to be taken into account when considering transgene expression for industrial microbial productions.