The Proteins of CRISPR

A short summary of the proteins involved in CRISPR.

 

In my CRISPR summary, I did not go into detail about how the technology uses proteins to cut the DNA. This post goes into more detail regarding them.

The main protein involved in the CRISPR ‘cutting’ complex is Cas9 (literally CRISPR Associated Protein 9). The other two main protein types involved are zinc finger nucleases and TALEN proteins. Below, I shall outline a brief summary of these three types alongside an overview of their mechanism of action.

Cas9: Imagine you’re hosting a very important party and you’ve spent absolutely ages selecting your outfit so that you stand out. Then you discover that people attending the party also have the exact same outfit. If you didn’t keep a cool head, you’d likely lash out at the other people. Well, that’s basically what Cas9 does. There is a guide sequence of RNA (ribonucleic acid instead of deoxyribonucleic acid – DNA) which Cas9 compares with DNA sequences. If the DNA sequence matches the guide sequence, then Cas9 cuts it. (I should emphasise here that by ‘matching’ I do not mean they are identical – I will cover complementary DNA in a future post). This is why Cas9 is so useful for CRISPR. If a scientist needs the DNA cutting at a specific location, they can create a guide sequence which matches it, and Cas9 will then cut the DNA where they need it to.

Zinc Finger Nuclease: Now there’s a protein name to make you giggle. It almost sounds like some sort of glove a superhero might have, doesn’t it? These are not natural – they are artificially synthesised in a lab. Zinc fingers are actually small proteins which contain zinc to make them stable. These are engineered by scientists to target a specific section of DNA, and trigger its cutting or repair at that location.

TALEN: This stands for Transcription Activator-Like Effector Nucleases. I’m sure you can see why it gets shortened to TALEN. Who has the time for such a long name? The transcription activator-like effector (TALE) can bind to pretty much any sequence of DNA which a scientist engineers it to be able to, so combining it with a nuclease (N) makes the overall TALEN protein. The TALE allows it to bind, and the N cuts the DNA at this point. Hence why they’re also really useful in CRISPR.

Obviously, there are other proteins being trialled and tested for CRISPR use (and other gene editing techniques). But Cas9 is the main protein involved, and the other two are also pretty handy. Proteins are more than just the thing you get when you eat meat or down those shake drinks they sell at the gym. They’re really important little things and I am going to be doing many more posts which involve proteins in the future. Now there’s something to look forward to.

 

 

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