MUTATIONS AFFECTING EXTRACELLULAR PROTEASE PRODUCTION IN THE FILAMENTOUS FUNGUS ASPERGILLUS-NIDULANS

The extracellular proteases of Aspergillus nidulans are known to be re gulated by carbon, nitrogen and sulphur metabolite repression. In this study, a mutant with reduced levels of extracellular protease was iso lated by screening for loss of halo production on milk plates. Genetic analysis of the mutant showed that it contains a single, recessive mu tation, in a gene which we have designated xprE, located on chromosme VI. The xprE1 mutation affected the production of extracellular protea ses in response to carbon, nitrogen and, to a lesser extent, sulphur l imitation. Three reversion mutations, xprF1, xprF2 and xprG1, which-su ppress xprE1, were characterised. Both xprF and xprG map to chromosome VII but the two genes are unlinked. The xprF1, xprF2 and xprG1 mutant s showed high levels of milk-clearing activity on medium containing mi lk as a carbon source but reduced growth on a number of nitrogen sourc es. Evidence is presented that the xprE1 and xprG1 mutations alter exp ression of more than one protease and affect levels of alkaline protea se gene mRNA.