# CRISPR --- **CRISPR**, or "Clusters of Regularly Interspersed Short Palindromic Repeats" is a [[bacterial immune system|prokaryotic defense mechanism]] against [[bacteriophage]]. If the bacteria survives a phage infection then it can retain a bit of it's genetic code, and store it in it's own little library. A single bacteria can have dozens of spacers. This way, when another of the same type of phage infects the bacteria, it can recognize it and act quickly. ![[CRISPR.png]] - **Spacer DNA** is a small piece of phage DNA that the bacteria stores in its CRISPER array, and acts as a sort of historic record of previously fought off phages. - **crRNA** are the bacteria's copies of the spacers that it can bring to the Cas proteins. - **Cas proteins**, or "CRISPR associated sequences", are the proteins that do all the work in the CRISPR-Cas system - The **Cas 1** protein is the protein responsible for taking the little bit of the phage's DNA and stores it in the CRISPR library. - The **Cas 9** protein is the protein responsible for taking the crRNA from the CRISPR and using that to identify and destroy invading phage DNA. ___