Correction to: Nature Structural & Molecular Biology https://doi.org/10.1038/s41594-021-00601-w, published online 7 June 2021.

In the version of this article initially published, the text labels in Fig. 3c were inadvertently reversed. The top isoform was labeled “Isoform A” rather than “Isoform E,” and the bottom isoform was labeled “Isoform E” rather than “Isoform A.” The changes have been made to the HTML and PDF versions of the article.