Abstract (eng)
Living cells interpret and react to physicochemical stress signals using intracellular signal
transduction systems, often involving post-translational modifications (PTMs) mediated by
complex kinase-phosphatase networks. The high osmolarity glycerol (HOG) pathway in
Saccharomyces cerevisiae is a paradigm for mitogen-activated protein kinase (MAPK) and
stress signalling. Its central key regulator is the MAPK Hog1, a homolog of the mammalian
stress-activated protein kinase (SAPK) p38, which becomes activated upon increased
external osmolarity.
The Hog1-dependent hyperosmotic stress response not only includes transcriptional
regulation, but also affects the global phosphorylation pattern and thereby controls diverse
cellular processes, such as carbon metabolism, cell cycle regulation and the increase of the
intracellular concentration of small osmolytes. However, although this pathway has been
studied thoroughly for more than 20 years in regard to its purpose and function, the search for
Hog1 substrates is not complete.
This work is part of a project designed to comprehensively identify substrates of Hog1. In detail,
my thesis describes the impact of two kinases on the stress- and Hog1-dependent
phosphorylome. First, I could widely exclude crosstalk effects of MAPK Kss1, the central
regulator of the filamentous growth pathway, on the stress-responsive phosphorylation pattern.
Secondly, I investigated the extent of indirect regulation of Hog1-dependent phosphorylation
sites via the well-established Hog1 target Rck2, a calmodulin kinase (CaMK)-like MAPK-
activated protein kinase (MAPKAPK). As a key finding I identified Rck2 as a major effector
kinase downstream of Hog1. Finally, I integrated and compared the results obtained by two
commonly used mass spectrometry (MS) data analysis softwares, namely MaxQuant and
Proteome Discoverer, that apply differing identification and quantification algorithms. With this
approach, I was able to enhance the comprehensiveness of our data even further.