Molecular Biology of Fungal Amino Acid Biosynthesis Regulation

Amino acids are essential precursors for the ribosomal biosynthesis of proteins. In addition, amino acids are used as precursors of nonribosomal synthetic products including such important pharmaceutically relevant secondary metabolites as the β-lactam antibiotics or their derivatives of fungi (Brakhage 1998; see also Chap. 16, this Vol.). Most fungal cells prefer to acquire the 20 different amino acids for translation by uptake from the diet. Amino acid uptake primarily depends on the nutritional conditions and requires appropriate sensors and uptake systems. When the required amino acid is present in the cultivation medium, no further specific enzyme activities are needed. Numerous fungi are also able to produce and secrete proteases to explore additional nutritional sources. Induction of those activities might require starvation conditions (e.g., for nitrogen) as well as the presence of extracellular protein. Secreted proteases permit the extracellular degradation of proteins and, therefore, the production of extracellular amino acids (Ogrydziak 1993; Pavlukova et al. 1998). This is especially required in an environment lacking further nitrogen or carbon sources.