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'Aspergillus nidulans' provides a convenient model for studying gene regulation mechanisms in eukaryotes. In this study the regulation and secretion of extracellular proteases was the subject of some investigations around the regulation of gene expression in this organism. Extracellular proteases are secreted to the growth medium to break the polypeptide chains and facilitate their uptake. Amino acid residues in proteins can act as nitrogen, carbon and sulphur sources. Proteins do not appear as favourite nutrients and when preferred nitrogen, carbon and sulphur sources are present, extracellular protease enzymes are produced at low levels. There are major regulatory circuits in 'A. nidulans' which control the metabolism of different nutrients. Several regulatory genes have appeared to be involved in the control of extracellular protease production. These include areA, mediating nitrogen metabolite repression (Arst and Cove, 1973), creB and creC, affecting carbon catabolite repression (Hynes and Kelly, 1977) and xprE, a new putative regulatory locus involved in production of extracellular proteases production in response to carbon and nitrogen limitation (M.E. Katz, unpublished data). |
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