Nat. Biotechnol. 10.1038/nbt.3828; published online 13 March 2017; corrected after print 31 March 2017

In the version of this article initially published, in the Figure 1 legend, the following text was inserted: “(d), and the average FRET efficiencies in transfected COS-7 cells (e)”; in Figure 2d, the right-hand y axis was given as “PS fusion,” rather than “DOTAP fusion”; in text beneath Figure 2, figure callouts were corrected and additional text added as follows: “275 mM (Fig.1d,e)” should read “275 mM (Fig. 1d)”, “9 mM (Fig. 1e)” should read “9 mM (Fig. 1f)”, “FI exhibited no” should be “FI exhibited different FRET efficiencies in intact cells (Fig. 1e) and no,” “strength (Fig. 1c–f)” should be “strength (Fig. 1c,d,f),” “reach 50% in” should be “reach 50% change in”; in text beneath Figure 3, “MCS+ (Fig. 2e–g)” should be “MCS+ (Fig. 2e,f)”; in Figure 3 legend, “s.e.” should read “s.e.m.” The errors have been corrected in the HTML and PDF versions of the article.