NITROGEN, CARBON, AND PH REGULATION OF EXTRACELLULAR ACIDIC PROTEASESOF ASPERGILLUS-NIGER

Aspergillus niger secretes a number of enzymes, including proteases, i nto its culture fluid. The regulation of the two major acidic extracel lular proteases, pepA and pepB, was investigated using Northern analys es. Our data suggest that the regulation of pepA and pepB expression o ccurs predominantly at the level of mRNA content and that, while they are regulated in a similar manner, differences are also clear in their expression. Both genes were found to be under complex regulatory cont rol. The expression of the two genes could be turned off by the presen ce of good nitrogen or carbon sources in the media, and external prote in sources did not induce expression of either gene under conditions o f carbon and nitrogen repression. The pH of the medium also played a m ajor role in their regulation as the expression of both genes was comp letely turned off under alkaline conditions, even when grown in media lacking good nitrogen and carbon sources but containing proteins. We i solated clones containing 5' non-coding sequences of the pepA gene fro m a lambda genomic library with a pepA specific probe. Analysis and co mparison of the promoter sequences of the pepA and pepB genes revealed that both contain several putative AREA- and CREA-binding sites and t hey also share an 18-bp-long sequence which is 83% identical in these two genes.