CRISPR/cas9 genome editing is used to create an amino acid substitution at position 373 (glutamate to glutamine, GAG to CAG, E373Q) and a silent mutation in the Cas9 PAM site (Ala371A - GCC to GCT - to prevent additional editing). The mutation preserves the helical structure of the HExxH motif but prevents the generation of a reactive nucleophile at the zinc metalloprotease site. (J:309184)