REGULATION OF THE ESCHERICHIA-COLI LRP-GENE

Lrp (leucine-responsive regulatory protein) is a major Escherichia col i regulatory protein which regulates expression of a number of operons , some negatively and some positively. This work relates to a characte rization of lrp, the gene encoding Lrp. Nucleotide sequencing establis hed that the coding regions of lrp and trxB (encoding thioredoxin redu ctase) are separated by 543 bp and that the two genes are transcribed in opposite directions. In addition, we used primer extension, deletio n analyses, and lrp-lacZ transcriptional fusions to delineate the prom oter and regulatory region of the lrp operon. The lrp promoter is loca ted 267 nucleotides upstream of the translational start codon of the l rp gene. In comparison with a wild-type strain, expression of the lrp operon was increased about 3-fold in a strain lacking Lrp and decrease d about 10-fold in a strain overproducing Lrp. As observed from DNA mo bility shift and DNase I footprinting analyses, Lrp binds to one or mo re sites within the region -80 to -32 relative to the start point of l rp transcription. A mutational analysis indicated that this same regio n is at least partly required for repression of lrp expression in vivo . These results demonstrate that autogenous regulation of lrp involves Lrp acting directly to cause repression of lrp transcription.