Correction to: Nature Structural & Molecular Biology https://doi.org/10.1038/s41594-019-0284-0, published online 19 August 2019.
In the version of this article initially published, four references were missing. The references are as follows (numbered 13–16, with the original references 13 and 14 renumbered as 17 and 18, respectively, and reference citations renumbered accordingly in the text):
13. Gates, S.N. et al. Science 357, aan1052 (2017).
14. Deville, C. et al. Sci. Adv. 3, e1701726 (2017).
15. de la Peña, A.H., Goodall, E.A., Gates, S.N., Lander, G.C. & Martin, A. Science 362, eaav0725 (2018).
16. White, K.I., Zhao, M., Choi, U.B., Pfuetzner, R.A., Brunger, A.T. eLife 7, e38888 (2018).
The errors have been corrected in the HTML and PDF versions of the article.