Correction to: Nature Methods https://doi.org/10.1038/s41592-020-0797-9, published online 6 April 2020.

In the version of this article initially published, the concentration of the synthetic DNA oligo was given as 100 mM in Methods section “Labeling DNA oligos with N3-kethoxal in vitro.” The correct concentration is 100 µM. The error has been corrected in the HTML and PDF versions of the article.