{'fraction_non_alphanumeric': 0.03258145363408521, 'fraction_numerical': 0.02631578947368421, 'mean_word_length': 5.549180327868853, '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}}
Structural Insights into the Activity of Enhancer-Binding Proteins

Activators of bacterial σ54–RNA polymerase holoenzyme are mechanochemical proteins that use adenosine triphosphate (ATP) hydrolysis to activate transcription. We have determined by cryogenic electron microscopy (cryo-EM) a 20 angstrom resolution structure of an activator, phage shock protein F [PspF(1-275)], which is bound to an ATP transition state analog in complex with its basal factor, σ54. By fitting the crystal structure of PspF(1-275) at 1.75 angstroms into the EM map, we identified two loops involved in binding σ54. Comparing enhancer-binding structures in different nucleotide states and mutational analysis led us to propose nucleotide-dependent conformational changes that free the loops for association with σ54.