The physiological consequences of loss of tRNA thiolation in Saccharomyces cerevisiae

Abstract

Ubiquitin and ubiquitin-like proteins (UBLs) have a diverse array of functions that serve to regulate many cellular processes in eukaryotic cells. The ubiquitin-related modifier UrmI is a conserved UBL that, in addition to serving as a protein modifier, functions as a sulfur carrier in tRNA thiolation reactions. Urml is required for formation of the s2 moiety that is found as part of the more complex mcm5 s2 U34 modification on the anticodon wobble uridines of tGliUUC, of tGgluUUG and tLysUUU tRNAs in a variety of organisms. It has become increasingly clear that tRNA modifications serve to alter the properties of tRNA molecules, and that tRNA modifications can impact the translational regulation of gene expression, but how specific modifications are connected to cellular processes remains largely unknown. This work focuses on Urml-dependent tRNA modifications in Saccharomyces cerevisiae. This thesis describes the phenotypes of URM] pathway mutants, and describes the physiological consequences in cells that lack the ability to thiolate tRNAs: slow growth, impaired translation and the increased activation of at least one stress response pathway. This thesis also describes a condition, growth at 37°C, that results in a decrease in tRNA thiolation in wild type cells. This decrease in tRNA thiolation requires the activity of RNA polymerase III and is accompanied by decreased levels of proteins that are involved in the tRNA thiolation pathway. This decrease in tRNA thiolation may be an adaptive strategy used by cells under specific growth conditions, and is an example of the condition specific modulation of tRNA modification levels