The absence of branched-chain amino acid and growth rate control at the internal ilvEp promoter of the ilvGMEDA operon.

The question of whether the promoter ilvEp, located in the coding region of ilvM, the second structural gene in the ilvGMEDA operon, is subject to either amino acid- or growth rate-mediated regulation is examined. The experiments described here were performed with ilvEp-cat and ilvEp-lac fusions carried as single copies on the chromosome. The activity of the ilvEp promoter was found to respond neither to the availability of branched-chain amino acids nor to a wide range of growth rates between 35 to 390 min. In the absence of any known role for the products of the ilvGMEDA operon when repressing levels of branched-chain amino acids are present, there appears to be only a gratuitous role for the transcription at ilvEp.