Underproduction of the largest subunit of RNA Polymerase II causes temperature sensitivity, slow growth, and inositol auxotrophy in Saccharomyces cerevisiae

Abstract

In the yeast Saccharomyces cerevisiae, mutations in genes encoding subunits of RNA polymerase II (RNAPII) often gives rise to a set of pleiotropic phenotypes that includes temperature sensitivity, slow growth and inositol auxotrophy. In this study, we show that these phenotypes can be brought about by a reduction in the intracellular concentration of RNAPII. Underproduction of RNAPII was achieved by expressing the gene (RPO21), encoding the largest subunit of the enzyme, from the LEU2 promoter or a weaker derivative of it, two promoters that can be repressed by the addition of leucine to the growth medium. We found that cells that underproduced RPO21 were unable to depress fully the expression of a reporter gene under the control of the INO1UAS. Our results indicate that temperature sensitivity, slow growth and inositol auxotrophy is a set lead to the prediction that some of the previously identified RNAPII mutations that confer this same set of phenotypes affect the assembly/stability of the enzyme. We propose a model to explain the hypersensitivity of INO1 transcription to mutations that affect components of the RNAPII transcriptional machinery.