SITE-DIRECTED MUTAGENESIS OF THE FERRIC UPTAKE REGULATION GENE OF ESCHERICHIA-COLI

The 12 histidine and four cysteine residues of the Fur repressor of Es cherichia coil were changed, respectively, to leucine and serine by si te directed mutagenesis of the fur gene. The affects of these mutation s were measured in vivo by ligation of the mutated genes to a wild-typ e fur promoter followed by measurement of the ability of these plasmid s to regulate expression of a lacZ fusion in the aerobactin operon. In vitro affects were assayed by insertion of the mutated genes in the e xpression vector pMON2064 attended by isolation of the altered Fur pro teins and appraisal of their capacity to bind to operator DNA. The res ults suggest that cysteine residues at positions 92 and 95 are importa nt for the activity of the Fur protein.