CONSTRUCTION OF A LOW-SERINE-TYPE-CARBOXYPEPTIDASE-PRODUCT MUTANT OF ASPERGILLUS-ORYZAE BY THE EXPRESSION OF ANTISENSE RNA AND ITS USE AS AHOST FOR HETEROLOGOUS PROTEIN SECRETION

Using an antisense control strategy, we isolated an Aspergillus oryzae mutant that produced low levels of carboxypeptidases (CPases). The mu tant TFC-1 expressed the antisense RNA of the structural gene of CPase O and showed about 30% of the CPase activity in the parent strain. Ge l filtration analysis indicated that this mutant decreased the CPase a ctivities not only of CPase O but also of CPase O-1 and O-2. This resu lt indicated that the antisense RNA was able to control the expression of the CPase genes as a group. Using the mutant as a heterologous pro tein expression host that produced the low levels of CPases, a stable and higher level of lysozyme expression could be obtained compared wit h the wild-type. In vitro proteolytic degradation assay also demonstra ted that human lysozyme was degraded by purified CPase O.