ANALYSIS OF THE ROLE OF THE GENE BIPA, ENCODING THE MAJOR ENDOPLASMIC-RETICULUM CHAPERONE PROTEIN IN THE SECRETION OF HOMOLOGOUS AND HETEROLOGOUS PROTEINS IN BLACK ASPERGILLI

The function of the endoplasmic-reticulum-localized chaperone binding protein (BiP) in relation to protein secretion in filamentous fungi wa s studied. It was shown that the overproduction of several homologous and heterologous recombinant proteins by Aspergillus strains induces t he expression of bipA: the BiP-encoding gene from Aspergillus niger an d Aspergillus awamori. As this result could imply that BiP plays a rol e in protein overproduction, the effect of modulation of bipA gene exp ression on protein secretion was studied in several recombinant strain s expressing glucoamylase (glaA) fusion genes. For overproduction of B iPA in these strains, extra copies of the bipA gene under the control of an inducible promoter were introduced. To allow analysis of the eff ect of a decreased bipA expression level on protein secretion, replace ment of the wild-type gene for a bipA gene driven by the glaA promoter was attempted. However, this endeavour failed because of the lethalit y of this replacement. Although the final amount of secreted recombina nt protein did not change significantly in strains with increased BiPA levels, increased levels of unprocessed fusion protein were detected in the total protein extracts of these strains.