Widespread positive selection for mRNA secondary structure at synonymous sites in domesticated yeast

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mRNA secondary structure assumes a critical role in gene regulation, especially for translational efficiency. Previous studies have a growing appreciation of purifying selection for the conserved mRNA structure across lineages of different species. However, the effect of mRNA structure on positive evolution remains unclear. Here, we construct a large-scale dataset of single nucleotide polymorphisms (SNPs) at synonymous sites in the population of Saccharomyces cerevisiae , combined with the experimental assessment of mRNA structure, and perform empirical population genetics data analysis through unfolded site-frequency spectra. Our results suggest that functional mRNA stem drives faster evolution of increasing GC contents itself with the purpose of regulating translational speed, which is greatly influenced by length. At the synonymous site without codon usage bias, this kind of positive selection still exists. Furthermore, mRNA secondary structure is subject to positive selection widespread among the yeast genome, particularly related to mitochondria activities, which is possibly aimed to achieve a balance between cellular respiration and alcoholic fermentation precisely at a non-protein level. It is conducive to the adaption of the dramatic environment alterations from wild to man-made environments during the domestication.

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