Abstract

In an effort to develop an efficient expression and secretion system for heterologous proteins in Aspergillus nidulans, the PCR-amplified coding sequence for alkaline protease (AlpA) of A. oryzae was cloned into a fungal expression vector downstream of A. nidulans alcA (alcohol dehydrogenase) promoter to yield pRAAlp. Transformation of A. nidulans with pRAAlp gave stable transformants harboring various copy numbers (3 to 10) of integrated alpA gene, from among which 6 representatives were selected. On a medium containing 0.8% ammonium sulfate that represses the expression of the hosts own protease, the alcA promoter-controlled AlpA expression was strongly induced by threonine but repressed by glucose. The level of AlpA secretion was highest (approximately 666 mU/ml) in transformant ALP6 containing the largest copy number integrated alpA. However, the level of AlpA secretion was not necessarily proportional to the copy numbers of the integrated alpA genes. The N-terminal sequence of the secreted mature AlpA was determined to be Gly-Leu-Thr-Thr-Gln-Lys-Ser and its molecular mass to be approximately 34 kDa, indicating that AlpA is properly processed by the removal of 121 N-terminal amino acids.

• Keywords: Aspergillus nidulans; Aspergillus oryzae; akaline protease; expression; secretion