So hot its CRISPR

One of the hottest things in science right now is CRISPR. I guess some people are going to win a Nobel prize for it soon. CRISPR is a cool trick that many bacteria have, and have had for many millions of years, but it is one that we have only really appreciated for a few years.

Like us bacteria suffer from infection from viruses, indeed the environment on Earth is stuffed full of enormous numbers of viruses that infect not us but bacteria. Now, if we have been infected by, say, measles then a part of our immune system ‘learns’ what the measles virus looks like, and then we are immune to a second dose of the measles.

We thought our bodies were smart like this, but that bacteria weren’t. We were wrong. They have CRISPR.

It works as follows. One enzyme cuts out a small length of DNA from an invading virus. And it pastes it into the bacteria’s own DNA, to act as a memory of what the virus’s DNA looks like. This DNA is then copied and passed down to the bacterium’s daughter, grand-daughter, etc. These daughters, grand-daughters are then ready to fight infection by the same type of virus.

This is because of another enzyme that takes lengths of RNA made from the DNA that is now part of the bacteria’s DNA but has the DNA sequence of the original virus. This RNA made by the bacteria can recognise viral DNA, because the sequence of the RNA is the same as that of the virus. So using this RNA, enzyme can recognise viral DNA and attack it, destroying the virus.

The key point is that a bacterial cell contains a lot of DNA, 90% + of which is its own DNA, and which it does not want to attack. It needs to be able to discriminate between what is part of itself and what is the virus, in order to attack the virus. The piece of viral DNA cut-and-pasted into its own DNA allows it to do so.

So, CRISPR is very handy for bacteria, including some of those currently in your gut. But what about us? Can we use it? Hopefully yes. It is a flexible way of editing DNA, so may have huge potential for the treatment of genetic diseases. Clearly if we could get it to edit the faulty gene of someone with a genetic disease like muscular dystrophy, we could cure them. This is a long way off, but scientists have shown they can treat a genetic disease of the liver in mice, so we’re making progress.

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