The Aspergillus midulans xprF gene encodes a hexokinase-like protein involved in the regulation of extracellular proteases

The extracellular proteases of Aspergillus nidulans are produced in respons e to limitation of carbon, nitrogen, or sulfur, even in the absence of exog enous protein. Mutations in the A. nidulans xprF and xprG genes have been s hown to result in elevated levels of extracellular protease ill response to carbon limitation. The xprF gene was isolated and sequence analysis indica tes that it encodes a 615-amino-acid protein, which represents a nerv type of fungal hexokinase or hexokinase-like protein. In addition to their catal ytic role, hexokinases are thought to be involved in triggering carbon cata bolite repression. Sequence analysis of the xprF1 and xprF2 alleles showed that both alleles contain nonsense mutations. No loss of glucose or fructos e phosphorylating activity was detected in xprF1 or xprF2 mutants. There ar e two possible explanations for this observation: (1) the xprF gene may enc ode a minor hexokinase or (2) the xprF gene may encode a protein with no he xose phosphorylating activity. Genetic evidence suggests that the xprF and xprG genes are involved in the same regulatory pathway. Support for this hy pothesis was provided by the identification of a new class of xprG(-) mutat ion that suppresses the xprF1 mutation and results in a protease-deficient phenotype.