Experimental proof for the regulation of Salmonella typhimurium purB by purR

Salmonella typhimurium purB encodes adeny-losuccinate lyase (ASL), the enzyme that catalyzes step 8 in the pathway for de novo synthesis of inosine 5’-monophos-phate (IMP) and also the final reaction in the two-step sequence from IMP to adenosine monophosphate (AMP). The nucleotide sequence ofpurB was obtained by the genetic map and sequence homologous analysis. The conserved pur operator in purB was identified to be located 185 bp downstream of the initiation codon and overlaps codons 62 - 67 in the protein-coding region. The binding of PurR to this operator was demonstrated by gel retardation experiment and site-directed mutagenesis, indicating that the purB is under the control of purR. We also answered why previous study had conflicting report concerning the regulation of purB by purR by identifying the junction site of purB to lacZ in a purB-MudJ (lacZ, Kan’) fusion strain. This result strongly supports that the purB is the second gene in the ycfC-purB operon.

Salmonella typhimurium purB encodes adenylosuccinate lyase (ASL), the enzyme that catalyzes step 8 in the pathway forde novo synthesis of inosine 5′-monophosphate (IMP) and also the final reaction in the two-step sequence from IMP to adenosine monophosphate (AMP). The nucleotide sequence ofpurB was obtained by the genetic map and sequence homologous analysis. The conservedpur operator inpurB was identified to be located 185 bp downstream of the initiation codon and overlaps codons 62 – 67 in the protein-coding region. The binding of PurR to this operator was demonstrated by gel retardation experiment and site-directed mutagenesis, indicating that thepurB is under the control ofpurR. We also answered why previous study had conflicting report concerning the regulation ofpurB bypurR by identifying the junction site ofpurB tolacZ in apurB- MudJ (lacZ,Kan r) fusion strain. This result strongly supports that thepurB is the second gene in theycfC-purB operon.