In-cell architecture of an actively transcribing-translating expressome

In bacteria, RNA polymerases can associate with ribosomes to form transcription-translation units called expressomes. Multiple models based on structural data of in vitro reconstitution assays have been proposed for how the two machineries interface with one another. Understanding this bacteria-specific coupling mechanism offers insight regarding the central dogma of molecular biology and might be leveraged for antibiotic development. O’Reilly et al. found that the NusA protein interfaces between the two complexes. The authors combined cryo–electron tomography and cross-linking mass spectrometry to produce an integrative model of the transcribing, translating expressome of Mycoplasma pneumoniae obtained entirely from in-cell data. This approach contributes to the development of in-cell structural biology.