Fig. 8

A possible model for the interaction between A. nidulans PkaA and SnfA during carbon catabolite repression (CCR) repressing (glucose) and de-repressing (cellulose) conditions. In the presence of glucose, A. nidulans PkaA is activated and represses SnfA. CreA is transported into the nucleus via importins where it represses either directly or indirectly the expression of cellulase-encoding genes (e.g., eglA) and their corresponding positive regulators (e.g., clrB). In the presence of cellulose, PkaA is inactive whereas SnfA is activated and probably mediates the phosphorylation and re-localization of CreA into the cytoplasm, resulting in cellulose gene de-repression. It is unknown whether SnfA is transported into the nucleus or if there is another intermediary protein that is phosphorylated by SnfA and which is responsible for CreA removal from the nucleus. The role played by nuclear importins/exportins during these processes also remains unknown. PkaA activity affects hyphal morphology, protein secretion and glucose transport