Introduction to CRISPR-Cas

What is CRISPR and Cas?

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, it is pronounced as CRISPER. CRISPR is a collection of genomic DNA sequences found in bacteria and archaea. Cas stands for CRISPR-associated protein, Cas is an enzyme that can cut up DNA and RNA, it has a role in the bacterial defence system. 

What does this info have to do with anything?!

Well, when bacteria are invaded by bacteriophages (viruses that infect bacteria), viral DNA from the specific bacteriophage is inserted into the bacterial genome at a position called the CRISPR locus in a process called Foreign DNA Acquisition. Then CRISPR RNAs (crRNA) are made from the CRISPR locus in the transcription phase. Now if the bacteria is invaded by that specific bacteriophage again, a specific crRNA will be made and used together with Cas to disrupt the foreign sequences. The crRNA is used to find the viral DNA as it is complementary to the viral sequences and then Cas will cut the foreign DNA, thereby disrupting the invasion and providing immunity. This is generally how the CRISPR-Cas system acts as a defence mechanism in bacteria and archaea. 

The image below summarises this process. 

last updated on 03-May-2020

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