One of our major aims is to understand the cogs and wheels of phosphorylation-modulated signal transduction machineries in the yeast S. cerevisiae. In this field, important still unresolved questions concern the dynamic interactions between different signaling factors and their effectors - e.g. in what cellular context they might happen, how they are controlled by phosphorylation events and how these interactions change during signaling events.

To approach these questions we have established and optimized a novel enzyme based protein proximity assay. This assay is based on a mammalian histone methyl-transferase and its highly specific substrate, the N-terminal fragment of histone 3. Apart from successfully characterizing known protein interactions in well studied signal systems such as the high osmolarity response, we have also started to use this approach for validating protein interactions that have been suggested by quantitative mass spectrometry and/or by genetic data.

A second project deals with the problem of how cell cycle dependent signals coordinate the transcriptional regulation of genes. In this case we have focused on the regulation of the main mitotic cyclin gene CLB2 in yeast. This gene is repressed in the G1-phase of the cell cycle, it is de-repressed at the START of S-phase and fully induced by a positive feedback mechanism during G2-phase and mitosis. In addition we have found that genotoxic and replication stress will suppress the activation of CLB2 as well as additional genes that exhibit similar G2/M specific expression patterns. We have therefore addressed the question of how phosphorylation events affect stability and function of the important transcriptional regulators, and how their specific modifications can be correlated with changes in the underlying chromatin structure and chromatin modification patterns.