Gene expression noise refers to the stochastic variation in the expression level of a gene among iso-genic cells under the same condition. Previous studies showed that the level of expression noise var-ies substantially among genes, is determined genetically, and is selectable. In this talk I address two questions on gene expression noise. First, I present evidence for adaptive elevation of expression noise in a group of plasma-membrane transporters in the budding yeast Saccharomyces cerevisiae and offer a mathematical model explaining why and when high noise may be beneficial. Second, using the flux balance model of metabolic networks, I estimate the deleterious effect of expression noise on the growth rate of yeast cells and show that gene expression noise lowers the maximal fit-ness as well as the efficacy of natural selection. Thus, expression noise is a two-edged sword that can be both advantageous and deleterious.
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