A mutation in the putative CRP binding site of the promoter of serovar Typhimurium enables growth with low orotate concentrations.

and use the inner membrane transporter DctA to import the pyrimidine biosynthetic pathway intermediate orotate from the environment. To study the regulation of expression, we used an serovar Typhimurium pyrimidine auxotroph to select a mutant that could grow in an otherwise nonpermissive culture medium containing glucose and a low concentration of orotate. Whole genome sequencing revealed a point mutation upstream of in the putative cyclic AMP receptor protein (CRP) binding site. The C→T transition converted the least favourable base to the most favourable base for CRP-DNA affinity. A transcriptional fusion confirmed that the mutant promoter gained responsiveness to CRP even in the presence of glucose. Moreover, expression was higher in the mutant than the wild type in the presence of alternative carbon sources that activate CRP.