Deoxyribonucleic acid-binding studies on the hut repressor and mutant forms of the hut repressor of Salmonella typhimurium

Abstract

In Salmonella typhimurium the genes coding for the enzymes of histidine utilization (hut) are clustered in two adjacent operons, hutMIGC and hut(P,R,Q)UH. A single repressor, the product of the C gene, regulates both operons by binding at two operator sites, one near M and one in (P,R,Q). The deoxyribonucleic acid (DNA)-binding activity of the repressor was measured using DNA's containing separate operators. The repressor had greater activity when assayed using DNA containing the operator of the (P,R,Q)UH operon than when assayed using DNA containing the operator of the MIGC operon. The binding to either operator was absent in the presence of the inducer, urocanate. The DNA-binding activities were also determined for two super-repressors. The super-repressors had altered DNA-binding properties, although the self-regulated nature of the repressors complicated the analysis of the results. A purfication procedure for the wild-type repressor is presented. The purified repressor was somewhat unstable, and additional experiments using it were not performed.