Global regulation of sulfur assimilation in Neurospora

Abstract
A complex regulatory circuit controls expression of many permeases and enzymes involved in sulfur assimilation in the filamentous fungus Neurospora crassa. CYS3, the global positive-acting sulfur regulatory protein, turns on the expression of structural genes that encode sulfur enzymes when N. crassa cells are limited for sulfur. Expression of the cys-3 gene itself is highly regulated by negative-acting sulfur-controller scon genes and by autogenous regulation. The CYS3 protein is localized within the nucleus and contains a bZip DNA-binding motif and regions rich in alanine and in proline that appear to function in trans activation. Amino acid substitutions for basic or neutral amino acids in the bZip domain of CYS3 lead to significant changes in its DNA-binding activity. Key words: sulfur regulation, CYS3, autogenous control, leucine zipper, trans activation.

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