Glucose is the main source of carbon and energy for most eukaryotic cells. This carbohydrate is also responsible for the regulation of important cellular and metabolic processes. The regulatory effects controlled by glucose are widespread in eukaryotic cell, including filamentous fungi, and are involved in the transport and phosphorylation of this sugar. However, the mechanisms involved in the sensing and signaling of extracellular glucose are not fully understood. In S. cerevisiae, it is known that the glucose sensing is regulated by a complex mechanism composed of sensor(s) and transporters, among others. In this organism 20 hexose transporters (Hxt proteins), which can be induced (low affinity transporters) or repressed (high affinity transporters) upon high and low glucose concentrations, respectively, have been described. The glucose sensing mechanism that activates the main glucose repression pathway requires the phosphorylation of this sugar. In this respect, the involvement of enzymes such as hexokinase (Hxk) and glucokinase (Glk) is necessary. In yeast glucose phosphorylation is catalyzed by Hxk-1, Hxk-2 and Glk1, but glucose repression requires only Hxk2. The pathway responsible for the induction of glucose transporters activity is mediated by two important sensors proteins called Snf3 and Rgt2. These two components are membrane proteins which are able to perceive extracellular glucose but unable to bind it. Thus, the role of Snf3 and Rgt2 in glucose sensing is to signal the presence of the carbohydrate and control the activity of Hxt transporters under low (Snf3) and high (Rgt2) sugar concentrations. Recently we identified four ORFs that showed homology to hexose sensors proteins from other fungi in the genome of the filamentous fungus Aspergillus nidulans: AN1797, AN10891, AN6669 and AN8737. We propose to delete the identified ORFs and to create null, double and triple mutants from these transporters in A. nidulans. To phenotypically characterize the mutants, their capacity of grow and uptake sugar in presence of different carbon sources will be analyzed. We also propose to identify low and high affinity glucose transporters through microarray analysis, using cDNA from fungal cultures grown at different glucose concentration.
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