As the list of genetic diseases that could be cured by gene
therapy continues to grow, a concern for scientists has been how
to best deliver modified genes to patients. The challenges in
this area are many—from delivery to preventing immune responses.
But perhaps the most basic challenge is how to best replace an
existing stretch of DNA with a new one—targeted mutagenesis.
Existing methods of targeted mutagenesis, while effective, also
have the side effect of changing other, related spots in the
genome. Kim and his colleagues have put to rest that concern,
however, with the development of a nickase, an enzyme that
breaks a single strand of DNA at a time to introduce new genetic
material. Because a nickase cuts only one strand—rather than
standard nucleases that cut both at once—unwanted nicks will be
quickly repaired by the cell’s built-in single strand break
repair system. At the desired mutagenesis site, a new strand of
DNA will be integrated into the genome by the repair system. The
South Korean research g