Table 1. Summary of SapI nicking variants.
| Nt.SapI-1 (E250K) | Top strand nicking |
| Nt.SapI-2 (K273R) | Top-strand nicking |
| Nt.SapI-3 (Q240R) | Top-strand nicking |
| Nt.SapI-4 (G271R) | Top-strand nicking |
| Nb.SapI-1 (D34Y/I82V/P168L/R420I) | Bottom-strand nicking |
| R420Na | Nicking phenotype in the context of R340H |
| R420S | Nicking phenotype in the context of T248A |
| R420C | Nicking phenotype |
| R420T | Nicking phenotype in the context of I213V |
| R420L | Nicking phenotype in the context of A71V/T401A |
| R420V | Nicking phenotype |
| R420A | Nicking phenotype in the context of D135G |
| R420G | Nicking phenotype in the context of E243G/L424H |
SapI amino acid substitutions resulting in a DNA nicking phenotype. Single variants E250K, G271R or K273R were created by site-directed mutagenesis using oligonucleotides listed in the Materials and Methods. Variant Q240R was selected directly without any accompanying substitutions. The substitution R420I was studied within the context of the other Nb.SapI-1 substitutions.
aAdditional substitutions at R420 were created by codon randomization (see Materials and Methods).