Genome Editing

The term "genome editing" refers to the application of techniques that allow a strand of DNA to be cut at a precisely defined location, thereby modifying the DNA by changing, removing or adding DNA sequences. The best known techniques of this kind include CRISPR/Cas9, ZFN and TALEN, which in this context are often referred to as "gene scissors".

CRISPR/Cas9 consists of two parts: The protein Cas9 is an enzyme with a so-called nuclease activity that enables it to completely cut through a DNA strand. Such enzymes are called restriction enzymes (also: restriction endonucleases, REN). CRISPR is an RNA molecule that binds to a precisely defined position on the DNA and thereby indicates the interface to the Cas9 nuclease. The particular advantage of CRISPR/Cas9 is that RNA molecules can be produced inexpensively and comparatively easily, making them easily accessible for research.

The zinc finger nuclease (ZFN) is a synthetic restriction enzyme. This consists of a zinc finger domain, which has the function of finding and binding to the corresponding DNA sequence, and a nuclease domain that cuts the DNA. 

TALEN (transcription activator-like effector nucleases) is also a synthetic restriction enzyme. Similar to zinc finger nuclease, it consists of a DNA-binding TAL-effector domain and a nuclease domain for cutting the DNA. 

In contrast to CRISPR/Cas9, both ZFN and TALEN have to be redesigned for each application to allow sequence-specific binding to DNA, which makes them much more complex to produce. 

Further information on the therapeutic potential of ZFN, TALEN and CRISPR/Cas9:

Gaj, Thomas / Gersbach, Charles A. / Barbas, Carlos F. (2013): ZFN, TALEN and CRISPR/Cas-based methods for genome engineering. In: Trends in Biotechnology 31 (7), 397–405. doi: 10.1016/j.tibtech.2013.04.004 Online Version

On the specific application of CRISPR/Cas9 see also:

Doudna, Jennifer A. / Charpentier, Emmanuelle (2014): The new frontier of genome engineering with CRISPR-Cas9. In: Science 346 (6213), 1258096. doi: 10.1126/science.1258096 Online Version

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