Regulation of sulfur and nitrogen metabolism in filamentous fungi.

In the filamentous fungi, N. crassa and A. nidulans, complex regulatory circuits control nitrogen metabolism and sulfur metabolism. The expression of entire sets of unlinked structural genes that encode metabolic enzymes is repressed when favored sulfur or nitrogen sources are available. These structural genes are coregulated by global positive-acting regulatory proteins and often are also controlled by metabolic inducers and pathway-specific regulatory proteins. The recent isolation of regulatory genes and representative structural genes of these circuits has provided significant new insight into the operation of both the nitrogen and the sulfur regulatory circuits, which involve sequence-specific DNA binding proteins, promoter control elements, metabolic inducers and repressors, and autogenous regulation.