{'fraction_non_alphanumeric': 0.027852650494159928, 'fraction_numerical': 0.012578616352201259, 'mean_word_length': 5.054347826086956, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
The structural basis for the self-inhibition of DNA binding by apo-σ70

Initiation of transcription in Escherichia coli is facilitated by promoter specificity factors, such as σ70, which bind promoter dsDNA when in complex with RNA polymerase (RNAP), in which it is in an extended conformation with solvent-exposed DNA-interacting residues. If so, what in the structure of apo-σ70 prevents binding to promoter dsDNA at high affinity? By performing cross-linking mass spectrometry (CL-MS) and integrative structural modelling we elucidate structure models of apo-σ70 that exhibit burial of almost all DNA-binding residues. In vivo CL-MS detects crosslinks unique to the compact fold of apo-σ70 that occur at stationary growth phase. Conclusively, we provide structural information to show that the high affinity DNA-binding capabilities of apo-σ70 are conformationally-inhibited and can be activated mostly in the context of transcription. One-Sentence Summary This work provides a structural mechanism for why apo-σ70 does not bind promoters at high affinity when it is not in the direct context of transcription.