RPG: Molecular Evolution of Gene Transcription in Evolved Strains of Yeast
9408317 Brown Differences in gene regulation in natural populations of organisms may serve as the most important source of genetic variation for the process of natural selection. The purpose of the proposed research is to investigate one of the molecular aspects of gene regulation, namely gene transcription, in response to positive selection, neutral mutation, and purifying selection. In a glucose-limited environment, genes engaged in glucose metabolism are under strong selection, and the genes for galactose metabolism are not used. Positive selection for enhanced glucose utilization may lead to increased activity of genes involved in galactose metabolism leading to the loss of galactose inducibility in these genes. In this environment, the sole nitrogen source is ammonium sulfate, and yeast must metabolize all amino acids. Genes for amino acid metabolism are critically important for cell growth, and their regulation is subject to purifying selection. The first objective of the proposed work is to assess the effect of positive selection on transcriptional regulation of genes whose products are involved in glucose metabolism; the effect of neutral mutations on the inducibility of genes whose products are involved in galactose metabolism, and the effect of purifying selection on the transcriptional regulation of genes involved in amino acid synthesis. The second objective is to determine whether nucleotide sequence differences in the promoter regions of genes may account for the transcriptional differences.