It depends upon the experimental design. Cas9 D10A will cut the target strand of DNA (which does not contain the PAM sequence), while Cas9 H840A will cut the non-target strand (which contains the PAM sequence). The availability and location of PAM sites within the target region of DNA needs to be assessed.
To learn more about the design and use of Cas9 nickases, refer to the application note at www.idtdna.com/CRISPR-Cas9 (Resources section).
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