FIG. 2.

Constitutive expression of the cysH operon in a cysK background. Strains MC530 (PcysH-lacZ) and MCK530 (PcysH-lacZ, cysK) (A) and DA642X (Pxyl-lacZ) and DA642X-K (Pxyl-lacZ, cysK) (B) were grown in sulfur-free minimal media supplemented with cystine, casein hydrolysate, and yeast extract. Cells were recovered by centrifugation and inoculated in sulfur-free minimal medium in the absence or presence of cystine. The addition of 5 mM 1,2,4-triazole or 0.8% xylose is indicated. Samples were taken 4 h after resuspension. β-Galactosidase activities are expressed in MU.