In Fig. 4d of this Letter, the band corresponding to free SUMO1 in the left-hand blot is incorrect, as it is a repeat of the band corresponding to free SUMO2 in the right-hand blot. Figure 1 of this Amendment shows the original incorrect panel and the corrected panel of Fig. 4d, for transparency to readers. The full uncropped blots are shown in the Supplementary Information to this Amendment. The original Letter has not been corrected.

Fig. 1 This figure displays the corrected and the incorrect published Fig. 4d of the original Letter. Full size image