The Aspergillus nigerGCN4 homologue, cpcA, is transcriptionally regulated and encodes an unusual leucine zipper

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Abstract
The general control transcriptional regulator gene cpcA of Aspergillus niger was cloned by complementation of a Saccharomyces cerevisiaeΔgcn4 mutant strain. The encoded protein conferred resistance to amino acid analogues when expressed in yeast. Disruption of cpcA in A. niger resulted in a strain which is sensitive towards 3-aminotriazole and fails to respond to amino acid starvation. cpcA encodes a transcript of ≈2400 nucleotides in length that includes a 5′ leader region of 900 nucleotides. The 5′ leader region contains two small open reading frames, suggesting translational control of gene expression. Steady-state mRNA levels of cpcA increase by a factor of three upon amino acid starvation. The coding region of cpcA is interrupted by a 57 bp intron and the deduced amino acid sequence displays an ≈30% overall identity to yeast GCN4p and Neurospora crassa cpc-1p. Critical amino acid residues of the transcriptional activation domains of GCN4p are conserved in cpcAp. The basic DNA-binding domain shows up to 70% amino acid sequence identity to other basic zipper (bZIP)-type transcriptional activators. cpcAp binds specifically to a GCN4p recognition element in gel retardation experiments. The C-terminal dimerization domain encodes a leucine zipper with only a single leucine residue.

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