The extracellular proteases of 'Aspergillus nidulans': a study of structural genes and their regulation

Abstract

Polyacrylamide gel electrophoresis and specific protease inhibitors were used to identify three serine proteases and one metallo-protease in the culture filtrate of 'A. nidulans' cultures subject to nutrient-limiting conditions. A gene encoding a putative acid protease was isolated from an 'A. nidulans' gene library using a heterologous probe. Sequence analysis showed that the 'A. nidulans' aspergillopepsin gene, designated prtB, shows similarity to the 'A. fumigatus' and 'A. niger' aspergillopepsin genes, with nucleotide identities of 67.7% and 54.8% respectively. When the putative PrtB protein sequence was compared to the protein sequences of other aspergillopepsin genes, it was found that although the active sites were conserved, there was an 8 amino acid deletion prior to the second active site. It is unknown what effect this deletion has on the function of the PrtB protein. No prtB transcript was detected, using Northern analysis or RT-PCR, in RNA obtained from cultures subjected to 4 hours nitrogen limitation at pH 3 and pH 8. It is possible that the 'A. nidulans' prtB gene is not expressed, or prtB may be expressed under conditions other than those tested.