DNA is inserted, replaced, or removed from a genome using artificially engineered nucleases, or "molecular scissors". The nucleases make specific double-strand breaks (DSBs) at desired places in the genome. The cell’s own mechanisms repair the induced break(s) by natural processes.
To understand the function of a gene or a protein one interferes with it in a sequence-specific way, and watches its effects on the organism. However, in some organisms it is difficult or impossible to do site-specific mutation. Therefore more indirect methods have to be used. Examples are:
- Silencing the gene of interest by short RNA interference (siRNA). Yet gene disruption by siRNA can be variable and incomplete.
- Genome editing with nucleases such as ZFN. This is different from siRNA. The engineered nuclease (the enzyme which cuts the DNA) is able to modify DNA-binding. Therefore it can in principle cut any targeted position in the genome, and introduce change the sequences for genes which cannot be specifically targeted by conventional RNAi.
The CRISPR/Cas9 method[change | change source]
In 2017 this system was announced as one of the biggest scientific achievements of the year. Cas9 is an enzyme which with a guide RNA, can put a new sequence of DNA into a genome. Sir John Skehel said "That might allow you to knock out a particular gene in a cell, or introduce a particular gene, or correct a particular mutated gene that you want to work better".
References[change | change source]
- sometimes "genome editing with engineered nucleases" (GEEN)
- The four types are: zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), the CRISPR/Cas system, and engineered meganuclease re-engineered homing endonucleases.
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- Tan W.S. et al (2012). "Precision editing of large animal genomes.". Adv Genet 80: 37–97. doi:10.1016/B978-0-12-404742-6.00002-8. PMC 3683964. PMID 23084873.
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- Method of the Year 2011. Nat Meth 9 (1), 1-1.
- Gallagher, James 2015. Dawn of gene-editing medicine? BBC News Health. 
- Gallagher, James 2016. Scientists get 'gene editing' go-ahead. BBC News Health. 
- The biggest scientific developments of 2017, according to two scientists at the Royal Society of London.