The version of this paper originally published shows incorrect units for two plasmid concentrations. In the "Reagent Setup" section, the instructions for sgRNA-Cas9 plasmid should read "Adjust the concentration of each plasmid to 1 μg μl-1," rather than "to 1 μg ml-1." Similarly, all concentrations in the tables in Steps 49A, 49C, and 49D should be in μg μl-1 instead of μg ml-1. Please note that these units have not been corrected in the PDF and HTML versions of the protocol available online.