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Activators of bacterial sigma54-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, sigma54. By fitting the crystal structure of PspF(1-275) at 1.75 angstroms into the EM map, we identified two loops involved in binding sigma54. 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 sigma54.

Original publication




Journal article



Publication Date





1972 - 1975


Adenosine Triphosphate, Amino Acid Motifs, Amino Acid Sequence, Bacterial Proteins, Binding Sites, Cryoelectron Microscopy, Crystallography, X-Ray, DNA-Binding Proteins, DNA-Directed RNA Polymerases, Escherichia coli Proteins, Hydrolysis, Hydrophobic and Hydrophilic Interactions, Models, Molecular, Molecular Sequence Data, Mutation, PII Nitrogen Regulatory Proteins, Protein Conformation, Protein Folding, Protein Structure, Quaternary, Protein Structure, Secondary, Protein Structure, Tertiary, RNA Polymerase Sigma 54, Sigma Factor, Trans-Activators, Transcription Factors