TFIIS and GreB: Two Like-Minded Transcription Elongation Factors with Sticky Fingers

How the structurally distinct transcription factor TFIIS from eukaryotes and its bacterial counterpart GreB act to convert their cognate RNA polymerases into ribonucleases has been a longstanding question. Now, two new structures of these factors bound to their respective RNA polymerases (Opalka et al. and Kettenberger et al. [this issue of Cell]) suggest how they accomplish this feat.