Fitness effects ofcis-regulatory variants in theSaccharomyces cerevisiae TDH3promoter

Variation in gene expression is widespread within and between species, but fitness consequences of this variation are generally unknown. Here we use mutations in the Saccharomyces cerevisiae TDH3 promoter to assess how changes in TDH3 expression affect cell growth. From these data, we predict the fitness consequences of de novo mutations and natural polymorphisms in the TDH3 promoter. Nearly all mutations and polymorphisms in the TDH3 promoter were found to have no significant effect on fitness in the environment assayed, suggesting that the wild type allele of this promoter is robust to the effects of most new cis -regulatory mutations.