AMBIDEXTROUS TRANSCRIPTIONAL ACTIVATION BY SOXS - REQUIREMENT FOR THEC-TERMINAL DOMAIN OF THE RNA-POLYMERASE ALPHA-SUBUNIT IN A SUBSET OF ESCHERICHIA-COLI SUPEROXIDE-INDUCIBLE GENES

Purified MalE-SoxS fusion protein specifically stimulated in vitro tra nscription of the Escherichia coil zwf, fpr, fumC, micF, nfo, and sodA genes, indicating that activation of the superoxide regulon requires only SoxS. As in vivo, a 21 bp sequence adjacent to the zwf promoter w as able to activate transcription of an heterologous promoter in vitro . Activation of zwf and fpr transcription required the C-terminal doma in (CTD) of the RNA polymerase alpha subunit, while stimulation of fum C, micF, nfo, and sodA transcription was independent of CTD truncation . Thus, like the catabolite gene activator protein (CAP), SoxS is an ' ambidextrous' activator, activation only requiring the a CTD in a subs et of regulated promoters. Indeed, the -35 hexamers of the zwf and fpr promoters lie downstream of the respective MalE-SoxS binding sites, w hile the binding sites of fumC, micF, nfo, and sodA overlap their -35 promoter hexamers.