Can SpRY recognize any PAM in human cells?

The application of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas) can be limited due to a lack of compatible protospacer adjacent motif (PAM) sequences in the DNA regions of interest. Recently, SpRY, a variant of Streptococcus pyogenes Cas9 (SpCas9), was reported, which nearly completely fulfils the PAM requirement. Meanwhile, PAMs for SpRY have not been well addressed. In our previous study, we developed the PAM Definition by Observable Sequence Excision (PAM-DOSE) and green fluorescent protein (GFP)-reporter systems to study PAMs in human cells. Herein, we endeavored to identify the PAMs of SpRY with these two methods. The results indicated that 5′-NRN-3′, 5′-NTA-3′, and 5′-NCK-3′ could be considered as canonical PAMs. 5′-NCA-3′ and 5′-NTK-3′ may serve as non-priority PAMs. At the same time, PAM of 5′-NYC-3′ is not recommended for human cells. These findings provide further insights into the application of SpRY for human genome editing.