In bacteria, the activation of gene transcription at many promoters is simple and only involves a single activator. The cyclic adenosine 3′,5′-monophosphate receptor protein (CAP), a classic activator, is able to activate transcription independently through two different mechanisms. Understanding the class I mechanism requires an intact transcription activation complex (TAC) structure at a high resolution. Here we report a high-resolution cryo–electron microscopy structure of an intact Escherichia coli class I TAC containing a CAP dimer, a σ70–RNA polymerase (RNAP) holoenzyme, a complete class I CAP-dependent promoter DNA, and a de novo synthesized RNA oligonucleotide. The structure shows how CAP wraps the upstream DNA and how the interactions recruit RNAP. Our study provides a structural basis for understanding how activators activate transcription through the class I recruitment mechanism.
Bibliographical noteFunding Information:
We thank Y. Wang for constructing E. coli CAP and s70 plasmids, J. Wang for advice on converting the cryo-EM map to a charge density distribution map, and Y. Yang for his careful and critical reading of the manuscript. We also thank the staff of the Center for Structural Biology Facility at Yale University for computational support. This work was supported by grant GM22778 to T.A.S. from the NIH. T.A.S. is an investigator of the Howard Hughes Medical Institute. B.L. performed protein-sample preparations and complex assembly used in the structure determination, negative-stain transmission EM analysis, all model building, refinement, and structural analysis experiments. C.H. and Z.Y. designed the cryo-EM experiment. C.H. performed cryo-EM grid preparation, screening and optimization, high-throughput data collection, image processing, and map generation with input from R.K.H. and Z.Y. B.L. and T.A.S. designed the experiments. B.L. and T.A.S. principally wrote the manuscript with input from all. The 3D cryo-EM density map and the coordinates for the structure of the class I CAP-TAC have been deposited in the Electron Microscopy Data Bank and Protein Data Bank under the accession codes EMD-7059, EMD-7060, and 6B6H, respectively. The authors declare no competing financial interests.