The genetic determinants and phenotypic consequences of variation in translation termination efficiency in Saccharomyces cerevisiae

Abstract

Translation termination is a highly controlled process in the cell. In

Saccharomyces cerevisiae, various regulatory factors employ genetic and epigenetic mechanisms to control this process. I used a quantitative dual luciferase reporter assay to demonstrate a difference in translation termination efficiency between two different yeast

strains, BY4724 and RM11-1a. I then used a linkage mapping technique, X-QTL, to show that this difference is largely explained by a coding polymorphism in TRM10 (which encodes a tRNA-methylating enzyme) and a regulatory polymorphism in SUP45 (which encodes one of the translation termination factors). BY and RM carry variants of TRM10 and SUP45 with opposite effects on translation termination efficiency. These

variants are common among 63 diverse S. cerevisiae strains and are in strong linkage disequilibrium with each other. This observation suggests that selection may have favored allelic combinations of the two genes that maintain an intermediate level of translation termination efficiency.

[PSI+], the prion conformation of the S. cerevisiae translation termination factor Sup35p, is an epigenetic modifier of translation termination efficiency. It has been proposed that [PSI+] acts as a capacitor, releasing hidden genetic variation and generating heritable phenotypic variation with adaptive value. This hypothesis is based on observations that [PSI+] can create different growth phenotypes in strains with different genetic backgrounds by decreasing translation termination efficiency. However, genetic loci

underlying such [PSI+]-induced, background-dependent phenotypes have yet to be identified. Here, I used sup35C653R, a partial loss-of-function allele of the SUP35 gene to model [PSI+] effect on translational termination efficiency in BY and RM. I used X-QTL to identify a number of readthrough-dependent loci for the growth conditions tested. I further showed that variation in SKY1, an SR protein kinase, underlies a readthrough-dependent locus observed for growth on diamide and hydrogen peroxide. I found that the allelic state of SKY1 interacts with readthrough level and the genetic background to determine growth rate in these two conditions. I believe this study is an

effective step in understanding the mechanisms responsible for readthrough-dependent phenotypes. Extending this study to other strains, specifically strains shown to harbor [PSI+], would help in advancing our understandings of the genetic basis of the [PSI+]-dependent phenotypes.