Science ( IF 41.845 ) Pub Date : 2020-07-31 , DOI: 10.1126/science.abb3758 Francis J. O’Reilly, Liang Xue, Andrea Graziadei, Ludwig Sinn, Swantje Lenz, Dimitry Tegunov, Cedric Blötz, Neil Singh, Wim J. H. Hagen, Patrick Cramer, Jörg Stülke, Julia Mahamid, Juri Rappsilber
Structural biology studies performed inside cells can capture molecular machines in action within their native context. In this work, we developed an integrative in-cell structural approach using the genome-reduced human pathogen Mycoplasma pneumoniae. We combined whole-cell cross-linking mass spectrometry, cellular cryo–electron tomography, and integrative modeling to determine an in-cell architecture of a transcribing and translating expressome at subnanometer resolution. The expressome comprises RNA polymerase (RNAP), the ribosome, and the transcription elongation factors NusG and NusA. We pinpointed NusA at the interface between a NusG-bound elongating RNAP and the ribosome and propose that it can mediate transcription-translation coupling. Translation inhibition dissociated the expressome, whereas transcription inhibition stalled and rearranged it. Thus, the active expressome architecture requires both translation and transcription elongation within the cell.