The mechanism of trans-activation of the Escherichia coli operon thrU(tufB) by the protein FIS. A model.

Transcription of the thrU(tufB) operon is trans-activated by the protein FIS which binds to the promoter upstream activator sequence (UAS). Deletions of parts of the UAS and insertions show that optimal trans-activation requires occupation by FIS of the two FIS-binding regions on the UAS and specific helical positioning of these regions. On the basis of these and other data, a model for the mechanism of thrU(tufB) trans-activation by FIS is proposed. This model implies that the mechanisms underlying stimulation by FIS of two totally different processes: inversion of viral DNA segments and transcription of stable RNA operons, are essentially the same.