Characterization of a protease deficient strain of Penicillium roqueforti generated by heterologous plasmid integration: potential use for protein production.

A strain of Penicillium roqueforti was transformed with a plasmid which confers resistance to phleomycin. Stable transformants were selected. They all present a high resistance to the antibiotic. Their proteolytic activity was tested. One transformant is a proteolytic deficient strain unable to degrade casein. It is characterized by a tandem integration of the transformant vector in one site of the genome. The extracellular proteins profile of the strain reveals the absence of a 43 kDa polypeptide which probably corresponds to the aspartyl protease of Penicillium roqueforti. The aspA gene which encodes aspartyl protease is not expressed in the transformant and Southern analyses show that the aspA gene is not disrupted by the transformation vector.