Natural selection on cis and trans regulation in yeasts

Gene expression is regulated both by cis elements, which are DNA segments closely linked to the genes they regulate, and by trans activating factors, which are usually proteins capable of diffusing to unlinked genes. Understanding the patterns and sources of regulatory variation is crucial for understanding phenotypic and genome evolution. Here, we investigate the global patterns of gene expression evolution in Saccharomyces cerivisiae. We report statistical methods useful in quantifying cis and trans regulation using next generation sequencing data. Using these methods, measured genome-wide allele-specific expression by deep sequencing to investigate the genetic architecture of gene regulatory variation between two strains of Saccharomyces cerevisiae. We find that expression polymorphism in yeast is common for both cis and trans regulation, though trans variation is more common. Our detailed analyses of the effects of functional constraint on expression variation as indicated by measures such as protein connectivity, gene essentiality, and the ratio of nonsynonymous substitutions to synonymous substitutions clearly reveal that both classes of variation are under purifying selection, but trans variation is more sensitive to selective constraint. Comparing interspecific expression divergence between S. cerevisiae and S. paradoxus to our intraspecific variation suggests that natural selection strongly influences the patterns of variation we observe. Further analyses revealed that cis divergence is more frequently mediated by positive Darwinian selection than trans divergence, which is compatible with neutral evolution. Study the gene expression patterns in two strains of yeast (BY and RM)