Received: 1 March 2020
Accepted: 17 July 2020
Published in print: 11 September 2020
We thank the Rutgers University Cryo-EM Core facility, the University of Michigan Life Sciences Institute Cryo-EM Facility, the National Center for Cryo-EM Access and Training (supported by NIH grant no. GM129539, Simons Foundation grant SF349247, and New York state grants), and the Pacific Northwest Center for Cryo-EM (supported by NIH grant no. GM129547 and Department of Energy Environmental Molecular Sciences Laboratory) for microscope access; K. Kuznedelov and K. Severinov for plasmids; L. Minakhin, B. Nickels, and J. Winkelman for discussion; and E. Eng and H. Wei for assistance. Funding: This work was supported by University of California discretionary funds to G.B., University of Michigan discretionary funds to M.S., and NIH grant no. GM041376 to R.H.E. Author contributions: V.M. and G.B. prepared biomolecules. C.W., V.M., E.F., J.K., and M.S. collected data. C.W., V.M., J.K., M.S., and R.H.E. analyzed data. C.W., V.M., and R.H.E. prepared figures. R.H.E. designed experiments and wrote the manuscript. Data and materials availability: Cryo-EM micrographs have been deposited in the Electron Microscopy Public Image Archive Resource (EMPIAR accession codes 10467 and 10468). Cryo-EM maps and atomic models have been deposited in the Electron Microscopy Database (EMDB accession codes 21386, 21468, 21469, 21470, 21471, 21472, 21474, 21475, 21476, 21477, 21482, 21483, 21485, 21486, 21494, 22082, 22084, 22087, 22107, 22141, 22142, 22181, 22192, and 22193) and the Protein Data Bank (PDB accession codes 6VU3, 6VYQ, 6VYR, 6VYS, 6VYT, 6VYU, 6VYW, 6VYX, 6VYY, 6VYZ, 6VZJ, 6VZ2, 6VZ3, 6VZ5, 6VZ7, 6XDQ, 6XDR, 6XGF, 6XII, 6XIJ, 6X6T, 6X7F, 6X7K, and 6X9Q). Materials are available from the authors on request.