Frequently asked questions

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Is there a PAM sequence present in every gene?

This is a difficult question to answer. However, because the frequency of the dinucleotide “GG” is 5.21% in the human genome [1], it is reasonable to expect that most genes will contain at least the PAM sequence (NGG) of the S. pyogenes Cas9.


  1. Scherer S (2008) A short guide to the human genome. Cold Spring Harbor, NY:Cold Spring Harbor Laboratory Press. xiv, p173.