Control of yeast MAPK function by the dual specificity phosphatase Msg5.
Marta Flandez, Clara Bermejo, Eva Tapia, M. Jose Marin, Humberto Martin, Maria Molina
Microbiologia II, Universidad Complutense, Plaza Ramon y Cajal, Madrid, 28040, Spain
The yeast dual specificity protein phosphatase (DSP) Msg5 has been shown to act on the MAPK Fus3. It is though that it also regulates the MAPK Kss1, since overexpression of this phosphatase leads to a reduced amount of phospho-Kss1. We have shown that this DSP is produced as two isoforms due to alternative translation initiation, and is essential in keeping a low basal phosphorylation level of the cell integrity MAPK Slt2. However, the global impact of Msg5 on the response mediated by these MAPKs is still unknown. To test this, a transcriptomic analysis of cells lacking Msg5 has been carried out. Consistent with the increased level of phospho-Fus3 observed in msg5 mutants both in basal conditions and upon treatment with pheromones, a significant number of genes involved in mating are up-regulated in msg5 cells. Surprisingly, whereas the lack of Msg5 induces a high level of Slt2 phosphorylation in the absence of stimulus, the transcriptional response is much less intense than the expected for an activated cell integrity pathway. Although two hybrid and copurification experiments show that Kss1 and Msg5 interact, msg5 mutants do not display significant variations of either phospho-Kss1 or expression levels of genes under the control of this MAPK. Evidence will be presented showing that the two Msg5 isoforms display different specificities for the distinct MAPKs, suggesting the existence of a novel mechanism of regulation of MAPK signalling by DSPs.