Expression and compartmentation of the glucose repressor CRE1 from the phytopathogenic fungus Sclerotinia sclerotiorum

Abstract

The glucose repressor from the phytopathogenic fungus Sclerotinia sclerotiorum is encoded by the cre1 gene. Polyclonal antibodies were raised against a fusion protein (gluthathione S‐transferase) GST–CRE1 in order to study cre1 expression. Western blot analyses revealed that CRE1 synthesis is regulated by the nature of the extracellular carbon source. High CRE1 levels are induced by glucose and remain stable after transfer into pectin medium, suggesting the existence of post‐translational mechanisms which inactivate CRE1 to allow transcription of glucose‐repressed genes. Subcellular fractionation demonstrated that CRE1 is localized in the nuclei of glucose grown hyphae and in the cytoplasm when glucose is removed from the culture medium. CRE1 fused to green fluorescent protein (GFP) was introduced into Aspergillus nidulans. Fluorescence microscopy showed the nuclear localization of the GFP–CRE1 fusion protein according to the presence of glucose in the culture medium, suggesting homologous post‐translational regulations of glucose repressors in fungi. We propose that filamentous fungi regulate the activity of the glucose repressor by controlling its nuclear translocation.