The synthesis of RNA is highly regulated at all stages by transcription factors. As an essential transcription elongation factor, NusA has been studied biochemically for more than 30 years. However, until now no structural information has been available on NusA-RNAP complexes and the NusA interaction site on RNAP was a point of speculation. Determination of the structure of RNA polymerase in complex with NusA is helping us understand how NusA regulates transcription. The resulting model of RNA polymerase in complex with NusA has shed light on the transition from the initiation to elongation stages of transcription, and how NusA functions in promoting regulatory pausing and termination.