Ambidextrous transcriptional activation by SoxS: requirement for the C‐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 transcription of the Escherichia coli 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 was able to activate transcription of an heterologous promoter in vitro . Activation of zwf and fpr transcription required the C‐terminal domain (CTD) of the RNA polymerase alpha subunit, while stimulation of fumC 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 α CTD in a subset of regulated promoters. Indeed, the −35 hexamers of the zwf and fpr promoters lie downstream of the respective MalE–SoxS binding sites, while the binding sites of fumC micF nfo , and sodA overlap their −35 promoter hexamers.