cys-3, the positive-acting sulfur regulatory gene of Neurospora crassa, encodes a sequence-specific DNA-binding protein.

cys-3, the positive-acting master sulfur regulatory gene of Neurospora crassa, turns on the expression of an entire set of unlinked structural genes which encode sulfur-catabolic enzymes. cys-3 encodes a protein of 236 amino acid residues and contains a potential bipartite DNA-binding domain which consists of a leucine zipper and an adjacent highly basic region. Gel band mobility shift and DNA footprint experiments were used to demonstrate that the CYS3 protein, expressed in Escherichia coli, binds to three distinct sites in the 5' upstream DNA of cys-14, the structural gene for sulfate permease II. The CYS3 protein also binds to one distinct sequence element upstream of the cys-3 gene itself, which suggests an autoregulatory role for this protein. Two mutant CYS3 proteins, altered in the basic region of the DNA-binding domain, failed to bind to either the cys-14 or the cys-3 upstream recognition elements.