THE INTEGRATION OF NITROGEN AND CARBON CATABOLITE REPRESSION IN ASPERGILLUS-NIDULANS REQUIRES THE GATA FACTOR AREA AND AN ADDITIONAL POSITIVE-ACTING ELEMENT, ADA

The expression of the structural genes of the proline utilization clus ter of Aspergillus nidulans is repressed efficiently only when both re pressing carbon and nitrogen sources are present. Two hypotheses can a ccount for this fact, One is a direct or indirect competition mechanis m between the positive-acting AreA GATA factor, mediating nitrogen met abolite repression, and the negative-acting CreA protein, mediating ca rbon catabolite repression. The second is to propose that CreA prevent s the binding or activity of another, as yet unidentified, positive-ac ting factor, here called ADA. We show the second possibility to be the correct one, and we localize the new positive cis-acting element with in 290 bp of the prnD-prnB divergent promoter.