CRISPR- TIME TO EDIT DNA?

What is it ?

CRISPR is a prokaryotic immune system which enables bacteria to combat viruses and bacteriophages. The acronym itself stands for : Clustered Regularly Interspaced Small Palindromic Repeats. The « clustered Regularly interspaced« part of CRISPR refers to the spacer genes (DNA from viruses that have infected the bacterium before) whilst the « short palindromic repeats« refers to how within the CRISPR system, there are series of bases which are repeated at intervals. These bases (A,T,C,G) when read forward or backwards, will be read the same. This is why they are « palindromic «

How does it work ?

In order to fully understand how CRISPR works, we have to consider to scenarios. One scenario involves the bacterium being infected by a virus which it had not been infected by previously. The second scenario involves the same bacterium, having survived the previous infection, being infected once again.

Let’s consider the first scenario. The virus firstly injects its DNA into the bacterium. Within the bacterium, there are Cas genes. These genes are responsible for the production of Cas proteins when transcribed and translated (which occurs after the virus injects its DNA). These Cas proteins will then breakdown the DNA from the virus and will then create a copy of it which is then inserted into the CRISPR system.

When the same virus infects the bacterium again, what will happen is that there will be two transcriptions. The first one involves the transcription of a Cas gene in order to produce a different Cas protein whilst the second transcription involves the DNA from the virus (the spacer gene) ,which the bacterium had received from the previous infection, in order to produce a RNA copy. This RNA copy is used by the Cas protein in order to help it identify the DNA that has been injected by the virus so that it can then break it down.

Why is CRISPR useful ?

Unfortunately, there are many people around the world who suffer from inherited disorders, many of which are caused by one incorrect letter. They can range from being frustrating to life threatening (as is the case with diseases such as cystic fibrosis and Huntington’s disease). However, CRISPR can provide a solution to these inherited disorders by being able to cut out the gene responsible for it and replacing it with a healthy one.

The way that this technique works is by scientists using a Cas 9 protein  and guide RNA. The guide RNA is responsible for providing information to the Cas 9 enzyme on where to cut and what to cut. It is able to do this as the RNA bases within the guide RNA are complementary to the gene that is supposed to be cut by the Cas 9 protein.

In the same way, CRISPR can also be used to treat or cure other diseases. For example, scientists in Japan have managed to stop the replication of HIV-1 viruses by using CRISPR to disrupt genes which are essential for the virus to replicate. There are also scientists in China who have managed to increase the resistance to HIV in mice

However, a less obvious use of CRISPR is within food. There are certain regions in the world where famine is prevalent; this can be due to an array of physical, social, and economic factors. However, CRISPR can enable us to modify any feature of a fruit or vegetable. For example, we can change its nutritional value or its ability to cope with more extreme weather conditions in order to produce a greater yield of highly nutritious crops. Due to supply and demand, the increase in yield may lead to a decrease in overall global prices for the food; this makes it cheaper for many countries to import these crops. It is not just countries that import that will benefit. Exporters will benefit as well due to the fact that a decrease in price will lead to an increase in demand.

Lavan Suthaskaran

Photo Credits due to: Lavan Suthaskaran