PRODUCTION OF THE HOMOLOGOUS PECTIN LYASE-B PROTEIN IN 6 GENETICALLY DEFINED PROTEASE DEFICIENT ASPERGILLUS-NIGER MUTANT STRAINS

An expression cassette has been transformed into six protease-deficien t (prt) mutant strains of Aspergillus niger. Transformants were tested for improved production of the proteolytically susceptible PELB teste r protein. In four complementation groups (prtA, B, D and F) distinct improvement of PELB yield was observed. These in vivo experiments in s ingle prt mutants confirmed earlier in vitro PELB degradation data and demonstrated how the use of protease-deficient mutants can significan tly improve protein production in A. niger. The strong effects of seve ral prt alleles on the stability of the PELB tester protein have initi ated a more detailed genetical and molecular characterization of the p rt mutations. Mapping of the cloned protease genes pepA [I], B [II], C [IV], D [I], E [IV] and F [IV] indicated that none of the prt mutatio ns represent alleles of the presently cloned protease (pep) genes from A. niger. Analysis of the expression of the pep genes in prt strains demonstrated that the strongly reduced pro tease activities observed i n several prt mutants are not reflected by reduced transcription level s for a number of extracellular proteases. These results indicate that the mode of action of the prt genes constitute an interesting group o f new genetic functions which severely affect protease production, and as such improve protein production, in A. niger.