Mannosylphosphate transfer to cell wall mannan is regulated by the transcriptional level of the MNN4 gene in Saccharomyces cerevisiae

Mannosylphosphorylation is a major oligosaccharide modification that provides negative charge in the Saccharomyces cerevisiae cell wall. Although two genes, MNN6 and MNN4, which encode a mannosylphosphate transferase and its putative positive regulator, respectively, are involved in this modification, the amount of Mnn4p has been found to be a limiting factor for mannosylphosphorylation. The level of mannosylphosphorylation increased at late-logarithmic and stationary phases of cell growth, and this was correlated to the transcriptional enhancement of MNN4. We also find that mannosylphosphate transfer to mannan is negatively regulated by the protein kinase A pathway, while the presence of 0.5 M potassium chloride enhanced MNN4 transcription. This type of transcriptional regulation is observed in many stress response genes, implying that mannosylphosphate transfer is involved in the cellular response to a variety of stresses.