The role of promoter elements of a ribosomal protein gene in Saccharomyces cerevisiae under various physiological conditions

Determination of the core promoter regions of the Saccharomyces cerevisiae RPS3 gene

Ribosomal protein genes (RPG), which are scattered throughout the genomes of all eukaryotes, are subjected to coordinated expression. In yeast, the expression of RPGs is highly regulated, mainly at the transcriptional level. Recent research has found that many ribosomal proteins (RPs) function in multiple processes in addition to protein synthesis. Therefore, detailed knowledge of promoter architecture as well as gene regulation is important in understanding the multiple cellular processes mediated by RPGs. In this study, we investigated the functional architecture of the yeast RPS3 promoter and identified many putative cis-elements. Using beta-galactosidase reporter analysis and EMSA, the core promoter of RPS3 containing UASrpg and T-rich regions was corroborated. Moreover, the promoter occupancy of RPS3 by three transcription factors was confirmed. Taken together, our results further the current understanding of the promoter architecture and trans-elements of the Saccharomyces cerevisiae RPS3 gene.

Carbon source regulation of PIS1 gene expression in Saccharomyces cerevisiae involves the MCM1 gene and the two-component regulatory gene, SLN1

The Saccharomyces cerevisiae PIS1 gene encodes phosphatidylinositol synthase. The amount of phosphatidylinositol synthase is not affected by the presence of inositol and choline in the growth medium. This is unusual because the amounts and/or activities of other phospholipid biosynthetic enzymes are affected by these precursors, and the promoter of the PIS1 gene contains a sequence resembling the regulatory element that coordinates the inositol-mediated regulation (UASINO). We found that transcription of the PIS1 gene was insensitive to inositol and choline and did not require the putative UASINO regulatory sequence or the cognate regulatory genes (INO2 and OPI1). The PIS1 promoter includes sequences (MCEs) that bind the Mcm1 protein. Because the Mcm1 protein interacts with both the Sln1 and the Gal11 regulatory proteins, we examined the effect of mutant alleles of the MCM1 and SLN1 genes and carbon source on expression of the PIS1 gene. We found that expression of the PIS1 gene was reduced when cells were grown in a medium containing glycerol and increased when grown in a medium containing galactose relative to cells grown in a glucose medium. The glycerol-mediated repression of PIS1 gene expression required both the MCM1 gene and the MCEs, whereas the SLN1 gene was required for full galactose-mediated induction of a PIS1-lacZ reporter gene. Thus, PIS1 gene expression is unique among the phospholipid biosynthetic structural genes because it is uncoupled from the inositol response and regulated in response to the carbon source. This is the first example in yeast of a complete circuit linking a stimulus (carbon source) to gene regulation (PIS1) using a two-component regulator (SLN1).