Transcription antiterminator RfaH alternates between closed (inactive) and open (activated) conformation. In this issue of Cell, Burmann et al. show that opening is accompanied by dramatic all-α to all-β refolding of its C-terminal domain. Each of the folds has a distinct function: all-α-fold acts as a specificity determinant, directing RfaH to a small subset of operons, whereas the all-β-fold recruits ribosome, thereby coupling RfaH-stimulated transcription to translation.
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