Robustness analysis of HOG pathway related genes in Saccharomyces cerevisiae

Robustness analysis of HOG pathway related genes in Saccharomyces cerevisiaeDoryaneh Ahmadpour1, Lars-G\uf6ran Ottosson1, Markus Krantz2, Jonas Warringer1, Anders Blomberg1 and Stefan Hohmann1*1Department of Cell and Molecular Biology/Microbiology, G\uf6teborg University, S-405 30 G\uf6teborg, Sweden2 The Systems Biology Institute (SBI), Shibuya, Tokyo, JapanE-mail: doryaneh.ahmadpour@gmm.gu.seRobustness is a fundamental property of biological systems and crucial for their effective function under internal or external perturbations. For instance, it has been proposed that internal parameters such as gene expression have been optimized during evolution such that a given system has the observed robustness. The permissible ranges of internal parameters in the cells are not comprehensively understood since there has not been a technique to measure such parameters.“Genetic tug-of-war” (gTOW) [1] is a genetic screening approach that allows the determination of the upper limit copy number of genes, and thereby the upper permissible range of the level of gene expression. This method is based on a 2-micron plasmid vector containing the LEU2d allele with a very weak complementation activity and the gene of interest inserted as target gene. When the leu2 ura3 mutant yeast transformed with pTOW plasmids is cultured under leucine-limiting conditions, there will be a bias toward increasing the plasmid copy number to satisfy the requirement for leucine. On the other hand there will be an opposing bias toward decreasing the plasmid copy number if the target gene inhibits growth when a certain copy number is exceeded (i.e. it reaches its upper limit). Eventually as a result of the “tug-of-war” between these two selection biases cells with optimized plasmid copy number will accumulate. In this study we have applied the gTOW method on 29 HOG pathway genes in S. cerevisiae. The high osmolarity glycerol (HOG) MAPK pathway is essential for yeast survival in high osmolarity condition [2]. It consists of two branches that activate a MAPK (Hog1) to orchestrate part of the transcriptional response. The HOG pathway is the best understood osmoresponsive system in eukaryotes. The quantitative data provided by the gTOW method collating with the existing computational models [3] could be used to analyze the robustness and fragility of the pathway.1. Moriya H, et al., (2006), PLoS Genet 2(7): e1112. Hohmann S (2002), Microbiol Mol Biol Rev 66:3003. Klipp E, et al., (2005), Nat Biotechnol 23:97