Abstract

The plasmid pBAD22 lrp $\rm Cm\sp{R}$ carrying the lrp coding region immediately downstream from the $\rm p\sb{BAD}$ promoter was used to vary intracellular concentrations of Lrp. The expression of the genes serA and gltD was determined in the presence of different concentrations of Lrp. The results showed that expression of serA and gltD was proportional to Lrp concentration, indicating that Lrp activates gene expression. A comparison of the response of the genes serA and gltD to the variations in Lrp concentrations showed that the promoters of serA were more sensitive to Lrp than that of gltD. L-leucine's effects on Lrp's function were also investigated. Adding L-leucine to the minimal media decreased Lrp's activation of both serA and gltD. As for the plasmid-carried lrp gene, a decrease in expression was observed as L-serine (500 $\mu\rm g/ml)$ was added to glycerol minimal media.