Copper upregulation of cus1 (A), cus2 (B), and cus3 (C) during development. Strains were incubated on CF agar plates containing 0 μM (♦), 20 μM (▪), 40 μM (▴), or 60 μM (•) copper. The specific β-galactosidase activity in the cell extracts was determined as described in Materials and Methods. The results are the averages of data from three different experiments. The error bars indicate standard deviations. Note the differences in the scales.