Performing crosslinking mass spectrometry and intergrative structural modelling to elucidate, for the first time, structure models of apo-σ70. Conclusively, we provide structural information to show that most of the DNA-binding capabilities of apo-σ70 are conformationally-inhibited and can be activated mostly in the context of transcription. CL-MS performed in E. coli detects crosslinks unique to the compact fold of apo-σ70 occurring at stationary growth phase.