CRISPR in Prokaryotes
There are three main steps to the CRISPR/Cas system in Prokaryotes. The first step, Insertion, allows Cas1 and Cas2 to detect the foreign DNA, cleave a protospacer, and attach it to the target DNA. The next step, crRNA processing, can be carried out through 3 unique mechanisms, although the primary pathway is Type II. In Type II, the sequence is transcribed and cleaved by Cas9 and RNase III. In the final step, Interference, additional trimming occurs at the 5’ end and mature crRNAs are created. The target sequences then intereact wwith the PAM sequence before the invading DNA is degraded.