Want to design a CRISPR for genome editing? Here are the PAM sites you need to keep in mind:

The PAM site is the only sequence requirement when designing a specific guide RNA for the CRISPR, i.e. only sites in the genomic DNA next to a specific PAM motif could be targeted and edited. The PAM site is in the genomic DNA, not in the guide RNA. The presence or absence of this motif next to your favorite sequence is one of the major limitations of the CRISPR/Cas9 system. If a Cas9 would be utilized to cleave an allele with a mutation, the mutation must be next (within preferably 10nt) to a PAM site.

(The PAM site is needed for the bacterial CRISPR system to discriminate the bacterial and viral genome, since the PAM site is absent from the former but present in the latter.)

Here are the PAM sites for the currently used Cas9 enzymes, check if you find a good one next to your sequence of interest:

R: A or G, W: A or T
*Be careful with non-canonical PAM sites, at some sites there might be no activity
**Not yet available, will be available soon

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