Recently, new tools have enabled researchers to make precision modifications in just about any organism they want, with nucleotide-level precision, incredibly rapidly. Most work by introducing a double-stranded DNA break at a specific location, which the cell then repairs. The differences lie in how the systems introduce the break, and the ease with which new sequences can be targeted.
ZFNs: The first genomic-editing strategy uses custom DNA endonucleases called zinc-finger nucleases (ZFNs). Zinc fingers are transcription factors; each finger module recognizes three to four bases of sequence, and by mixing and matching those modules researchers can more or less target any sequence they wish.
TALENs: Transcription activator-like effector nucleases, or TALENs, are dimeric transcription factor/nucleases built from arrays of 33 to 35 amino acid modules, each of which targets a single nucleotide. By assembling those arrays just so, researchers can target nearly any sequence they like. Especially cheaper. Labs can build custom TALENs for a fraction of what ZFNs cost. Addgene sells individual TALEN plasmids for $65 apiece, and complete kits for a few hundred dollars. Dan Voytas’ popular Golden Gate TALEN 2.0 kit costs $425.
CRISPR/Cas: The new kid on the block, genome-editing-wise, is the so-called CRISPR/Cas system. The subject of tremendous excitement in the research community—of 480 papers in PubMed on the topic, 160 have been published this year—CRISPR/Cas is like a DNA-targeted form of RNA interference.