Nature 439, 234–238 (2006)

Details of the cryo-electron microscopy data set pertaining to the structure of Sec 13/31 reported in this Letter have now been deposited in the Electron Microscopy Database at the European Bioinformatics Institute under the accession number 1232 (http://www.ebi.ac.uk/msd-srv/emsearch/atlas/1232_downloads.html).