FIG. 4.
Effect of C4-dicarboxylates, C6-tricarboxylates, and related compounds on the expression of dcuB′-′lacZ in strains carrying wild-type DcuS, C4-dicarboxylate-specific DcuSDC(F141S), or citrate-specific DcuSCit(T101G F120M I125S). E. coli IMW260 (ΔdcuS) was transformed with low-copy plasmids containing alleles of dcuS encoding either DcuS, DcuSDC(F141S), or DcuSCit(T101G F120M). The bacteria were grown in the presence of the effectors (20 mM [5 mM for nitropropionate]), and β-galactosidase activity was measured at an OD578 of 0.5 to 0.8. The activities are the mean of at least six independent growth experiments and four repeats each. Fum, fumarate; Asp, aspartate; Tar, d-tartrate; Nipr, nitropropionate; Mes, mesaconate; Cit, citrate; Icit, isocitrate; Tcar; tricarballylate; Glr, glutarate.