PURIFICATION AND REGULATORY PROPERTIES OF MARA PROTEIN, A TRANSCRIPTIONAL ACTIVATOR OF ESCHERICHIA-COLI MULTIPLE ANTIBIOTIC AND SUPEROXIDE RESISTANCE PROMOTERS

Expression of the marA or soxS genes is induced by exposure of Escheri chia coli to salicylate or superoxides, respectively, This, in turn, e nhances the expression of a common set of promoters (the mar/soxRS reg ulons), resulting in both multiple antibiotic and superoxide resistanc e, Since MarA protein is highly homologous to SoxS, and since a MalE-S oxS fusion protein has recently been shown to activate soxRS regulon t ranscription, the ability of MarA to activate transcription of these g enes was tested, MarA was overexpressed as a histidine-tagged fusion p rotein, purified, cleaved with thrombin (leaving one N-terminal histid ine residue), and renatured, Like MalE-SoxS, MarA (i) activated the tr anscription of zwf,fpr,fumC, micF, nfo, and sodA; (ii) required a 21-b p ''soxbox'' sequence to activate zwf transcription; and (iii) was ''a mbidextrous,'' i.e., required the C-terminal domain of the alpha subun it of RNA polymerase for activation of zwf but not fumC or micF, Thus, the mar and soxRS systems use activators with very similar specificit ies and mechanisms of action to respond to different environmental sig nals.