The sulfur regulatory circuit of the filamentous fungus, Neurospora crassa,
consists of a set of unlinked structural genes which encode sulfur catabolic and two
major regulatory genes which govern their expression. The cys-3 regulatory gene
encode a transacting regulatory protein which activates the expression of cys-14 and
ars, whereas the other regulatory genes Scon-l and Scon-2 appear to act in a
negative fashion