Correction to: Nature Structural & Molecular Biology https://doi.org/10.1038/s41594-017-0016-2, published online 15 January 2018.

In the version of this article originally published, the value given for electron dose in Table 1 was incorrect. This value was originally stated as 4.8 but should have been 50. The error has been corrected in the HTML and PDF versions of the article.