Nature 520, 511–517 (2015); doi:10.1038/nature14367

In this Article, the raw micrographs shown in Extended Data Figs 4a and 5a were inadvertently identical images. The panel originally shown in Extended Data Fig. 4a is the correct one, and Extended Data Fig. 5a has now been corrected. This error does not alter any conclusions or statements associated with the study.