Derivatives of the yeast GCN4 transcription factor containing acidic regions of 35 to 40 amino acids fused directly to the DNA-binding domain are fully functional in vivo. High resolution deletion analysis and proteolytic mapping suggest that the activation region is a repeated structure composed of small units acting additively. Acidic character is a feature of the structural motif, possibly a dimer of alpha-helices from two GCN4 monomers, that may be important for interactions with the basic transcriptional machinery.